## What changes were proposed in this pull request?

This PR avoids to generate a huge method for calculating a murmur3 hash for nested structs. This PR splits a huge method (e.g. `apply_4`) into multiple smaller methods.

Sample program
```
  val structOfString = new StructType().add("str", StringType)
  var inner = new StructType()
  for (_ <- 0 until 800) {
    inner = inner1.add("structOfString", structOfString)
  }
  var schema = new StructType()
  for (_ <- 0 until 50) {
    schema = schema.add("structOfStructOfStrings", inner)
  }
  GenerateMutableProjection.generate(Seq(Murmur3Hash(exprs, 42)))
```

Without this PR
```
/* 005 */ class SpecificMutableProjection extends org.apache.spark.sql.catalyst.expressions.codegen.BaseMutableProjection {
/* 006 */
/* 007 */   private Object[] references;
/* 008 */   private InternalRow mutableRow;
/* 009 */   private int value;
/* 010 */   private int value_0;
...
/* 034 */   public java.lang.Object apply(java.lang.Object _i) {
/* 035 */     InternalRow i = (InternalRow) _i;
/* 036 */
/* 037 */
/* 038 */
/* 039 */     value = 42;
/* 040 */     apply_0(i);
/* 041 */     apply_1(i);
/* 042 */     apply_2(i);
/* 043 */     apply_3(i);
/* 044 */     apply_4(i);
/* 045 */     nestedClassInstance.apply_5(i);
...
/* 089 */     nestedClassInstance8.apply_49(i);
/* 090 */     value_0 = value;
/* 091 */
/* 092 */     // copy all the results into MutableRow
/* 093 */     mutableRow.setInt(0, value_0);
/* 094 */     return mutableRow;
/* 095 */   }
/* 096 */
/* 097 */
/* 098 */   private void apply_4(InternalRow i) {
/* 099 */
/* 100 */     boolean isNull5 = i.isNullAt(4);
/* 101 */     InternalRow value5 = isNull5 ? null : (i.getStruct(4, 800));
/* 102 */     if (!isNull5) {
/* 103 */
/* 104 */       if (!value5.isNullAt(0)) {
/* 105 */
/* 106 */         final InternalRow element6400 = value5.getStruct(0, 1);
/* 107 */
/* 108 */         if (!element6400.isNullAt(0)) {
/* 109 */
/* 110 */           final UTF8String element6401 = element6400.getUTF8String(0);
/* 111 */           value = org.apache.spark.unsafe.hash.Murmur3_x86_32.hashUnsafeBytes(element6401.getBaseObject(), element6401.getBaseOffset(), element6401.numBytes(), value);
/* 112 */
/* 113 */         }
/* 114 */
/* 115 */
/* 116 */       }
/* 117 */
/* 118 */
/* 119 */       if (!value5.isNullAt(1)) {
/* 120 */
/* 121 */         final InternalRow element6402 = value5.getStruct(1, 1);
/* 122 */
/* 123 */         if (!element6402.isNullAt(0)) {
/* 124 */
/* 125 */           final UTF8String element6403 = element6402.getUTF8String(0);
/* 126 */           value = org.apache.spark.unsafe.hash.Murmur3_x86_32.hashUnsafeBytes(element6403.getBaseObject(), element6403.getBaseOffset(), element6403.numBytes(), value);
/* 127 */
/* 128 */         }
/* 128 */         }
/* 129 */
/* 130 */
/* 131 */       }
/* 132 */
/* 133 */
/* 134 */       if (!value5.isNullAt(2)) {
/* 135 */
/* 136 */         final InternalRow element6404 = value5.getStruct(2, 1);
/* 137 */
/* 138 */         if (!element6404.isNullAt(0)) {
/* 139 */
/* 140 */           final UTF8String element6405 = element6404.getUTF8String(0);
/* 141 */           value = org.apache.spark.unsafe.hash.Murmur3_x86_32.hashUnsafeBytes(element6405.getBaseObject(), element6405.getBaseOffset(), element6405.numBytes(), value);
/* 142 */
/* 143 */         }
/* 144 */
/* 145 */
/* 146 */       }
/* 147 */
...
/* 12074 */       if (!value5.isNullAt(798)) {
/* 12075 */
/* 12076 */         final InternalRow element7996 = value5.getStruct(798, 1);
/* 12077 */
/* 12078 */         if (!element7996.isNullAt(0)) {
/* 12079 */
/* 12080 */           final UTF8String element7997 = element7996.getUTF8String(0);
/* 12083 */         }
/* 12084 */
/* 12085 */
/* 12086 */       }
/* 12087 */
/* 12088 */
/* 12089 */       if (!value5.isNullAt(799)) {
/* 12090 */
/* 12091 */         final InternalRow element7998 = value5.getStruct(799, 1);
/* 12092 */
/* 12093 */         if (!element7998.isNullAt(0)) {
/* 12094 */
/* 12095 */           final UTF8String element7999 = element7998.getUTF8String(0);
/* 12096 */           value = org.apache.spark.unsafe.hash.Murmur3_x86_32.hashUnsafeBytes(element7999.getBaseObject(), element7999.getBaseOffset(), element7999.numBytes(), value);
/* 12097 */
/* 12098 */         }
/* 12099 */
/* 12100 */
/* 12101 */       }
/* 12102 */
/* 12103 */     }
/* 12104 */
/* 12105 */   }
/* 12106 */
/* 12106 */
/* 12107 */
/* 12108 */   private void apply_1(InternalRow i) {
...
```

With this PR
```
/* 005 */ class SpecificMutableProjection extends org.apache.spark.sql.catalyst.expressions.codegen.BaseMutableProjection {
/* 006 */
/* 007 */   private Object[] references;
/* 008 */   private InternalRow mutableRow;
/* 009 */   private int value;
/* 010 */   private int value_0;
/* 011 */
...
/* 034 */   public java.lang.Object apply(java.lang.Object _i) {
/* 035 */     InternalRow i = (InternalRow) _i;
/* 036 */
/* 037 */
/* 038 */
/* 039 */     value = 42;
/* 040 */     nestedClassInstance11.apply50_0(i);
/* 041 */     nestedClassInstance11.apply50_1(i);
...
/* 088 */     nestedClassInstance11.apply50_48(i);
/* 089 */     nestedClassInstance11.apply50_49(i);
/* 090 */     value_0 = value;
/* 091 */
/* 092 */     // copy all the results into MutableRow
/* 093 */     mutableRow.setInt(0, value_0);
/* 094 */     return mutableRow;
/* 095 */   }
/* 096 */
...
/* 37717 */   private void apply4_0(InternalRow value5, InternalRow i) {
/* 37718 */
/* 37719 */     if (!value5.isNullAt(0)) {
/* 37720 */
/* 37721 */       final InternalRow element6400 = value5.getStruct(0, 1);
/* 37722 */
/* 37723 */       if (!element6400.isNullAt(0)) {
/* 37724 */
/* 37725 */         final UTF8String element6401 = element6400.getUTF8String(0);
/* 37726 */         value = org.apache.spark.unsafe.hash.Murmur3_x86_32.hashUnsafeBytes(element6401.getBaseObject(), element6401.getBaseOffset(), element6401.numBytes(), value);
/* 37727 */
/* 37728 */       }
/* 37729 */
/* 37730 */
/* 37731 */     }
/* 37732 */
/* 37733 */     if (!value5.isNullAt(1)) {
/* 37734 */
/* 37735 */       final InternalRow element6402 = value5.getStruct(1, 1);
/* 37736 */
/* 37737 */       if (!element6402.isNullAt(0)) {
/* 37738 */
/* 37739 */         final UTF8String element6403 = element6402.getUTF8String(0);
/* 37740 */         value = org.apache.spark.unsafe.hash.Murmur3_x86_32.hashUnsafeBytes(element6403.getBaseObject(), element6403.getBaseOffset(), element6403.numBytes(), value);
/* 37741 */
/* 37742 */       }
/* 37743 */
/* 37744 */
/* 37745 */     }
/* 37746 */
/* 37747 */     if (!value5.isNullAt(2)) {
/* 37748 */
/* 37749 */       final InternalRow element6404 = value5.getStruct(2, 1);
/* 37750 */
/* 37751 */       if (!element6404.isNullAt(0)) {
/* 37752 */
/* 37753 */         final UTF8String element6405 = element6404.getUTF8String(0);
/* 37754 */         value = org.apache.spark.unsafe.hash.Murmur3_x86_32.hashUnsafeBytes(element6405.getBaseObject(), element6405.getBaseOffset(), element6405.numBytes(), value);
/* 37755 */
/* 37756 */       }
/* 37757 */
/* 37758 */
/* 37759 */     }
/* 37760 */
/* 37761 */   }
...
/* 218470 */
/* 218471 */     private void apply50_4(InternalRow i) {
/* 218472 */
/* 218473 */       boolean isNull5 = i.isNullAt(4);
/* 218474 */       InternalRow value5 = isNull5 ? null : (i.getStruct(4, 800));
/* 218475 */       if (!isNull5) {
/* 218476 */         apply4_0(value5, i);
/* 218477 */         apply4_1(value5, i);
/* 218478 */         apply4_2(value5, i);
...
/* 218742 */         nestedClassInstance.apply4_266(value5, i);
/* 218743 */       }
/* 218744 */
/* 218745 */     }
```

## How was this patch tested?

Added new test to `HashExpressionsSuite`

Author: Kazuaki Ishizaki <ishizaki@jp.ibm.com>

Closes #19563 from kiszk/SPARK-22284.

(cherry picked from commit f2da738c76810131045e6c32533a2d13526cdaf6)
Signed-off-by: Wenchen Fan <wenchen@databricks.com>