### What changes were proposed in this pull request?

https://bugs.openjdk.java.net/browse/JDK-8170259
https://bugs.openjdk.java.net/browse/JDK-8170563

When we cast string type to decimal type, we rely on java.math. BigDecimal. It can't accept leading and training spaces, as you can see in the above links. This behavior is not consistent with other numeric types now. we need to fix it and keep consistency.

### Why are the changes needed?

make string to numeric types be consistent

### Does this PR introduce any user-facing change?

yes, string removed trailing or leading white spaces will be able to convert to decimal if the trimmed is valid

### How was this patch tested?

1. modify ut

#### Benchmark
```scala
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.spark.sql.execution.benchmark

import org.apache.spark.benchmark.Benchmark

/**
 * Benchmark trim the string when casting string type to Boolean/Numeric types.
 * To run this benchmark:
 * {{{
 *   1. without sbt:
 *      bin/spark-submit --class <this class> --jars <spark core test jar> <spark sql test jar>
 *   2. build/sbt "sql/test:runMain <this class>"
 *   3. generate result: SPARK_GENERATE_BENCHMARK_FILES=1 build/sbt "sql/test:runMain <this class>"
 *      Results will be written to "benchmarks/CastBenchmark-results.txt".
 * }}}
 */
object CastBenchmark extends SqlBasedBenchmark {

  override def runBenchmarkSuite(mainArgs: Array[String]): Unit = {
    val title = "Cast String to Integral"
    runBenchmark(title) {
      withTempPath { dir =>
        val N = 500L << 14
        val df = spark.range(N)
        val types = Seq("decimal")
        (1 to 5).by(2).foreach { i =>
          df.selectExpr(s"concat(id, '${" " * i}') as str")
            .write.mode("overwrite").parquet(dir + i.toString)
        }

        val benchmark = new Benchmark(title, N, minNumIters = 5, output = output)
        Seq(true, false).foreach { trim =>
          types.foreach { t =>
            val str = if (trim) "trim(str)" else "str"
            val expr = s"cast($str as $t) as c_$t"
            (1 to 5).by(2).foreach { i =>
              benchmark.addCase(expr + s" - with $i spaces") { _ =>
                spark.read.parquet(dir + i.toString).selectExpr(expr).collect()
              }
            }
          }
        }
        benchmark.run()
      }
    }
  }
}

```

#### string trim vs not trim
```java
[info] Java HotSpot(TM) 64-Bit Server VM 1.8.0_231-b11 on Mac OS X 10.15.1
[info] Intel(R) Core(TM) i9-9980HK CPU  2.40GHz
[info] Cast String to Integral:                  Best Time(ms)   Avg Time(ms)   Stdev(ms)    Rate(M/s)   Per Row(ns)   Relative
[info] ------------------------------------------------------------------------------------------------------------------------
[info] cast(trim(str) as decimal) as c_decimal - with 1 spaces           3362           5486         NaN          2.4         410.4       1.0X
[info] cast(trim(str) as decimal) as c_decimal - with 3 spaces           3251           5655         NaN          2.5         396.8       1.0X
[info] cast(trim(str) as decimal) as c_decimal - with 5 spaces           3208           5725         NaN          2.6         391.7       1.0X
[info] cast(str as decimal) as c_decimal - with 1 spaces          13962          16233        1354          0.6        1704.3       0.2X
[info] cast(str as decimal) as c_decimal - with 3 spaces          14273          14444         179          0.6        1742.4       0.2X
[info] cast(str as decimal) as c_decimal - with 5 spaces          14318          14535         125          0.6        1747.8       0.2X
```
#### string trim vs this fix
```java
[info] Java HotSpot(TM) 64-Bit Server VM 1.8.0_231-b11 on Mac OS X 10.15.1
[info] Intel(R) Core(TM) i9-9980HK CPU  2.40GHz
[info] Cast String to Integral:                  Best Time(ms)   Avg Time(ms)   Stdev(ms)    Rate(M/s)   Per Row(ns)   Relative
[info] ------------------------------------------------------------------------------------------------------------------------
[info] cast(trim(str) as decimal) as c_decimal - with 1 spaces           3265           6299         NaN          2.5         398.6       1.0X
[info] cast(trim(str) as decimal) as c_decimal - with 3 spaces           3183           6241         693          2.6         388.5       1.0X
[info] cast(trim(str) as decimal) as c_decimal - with 5 spaces           3167           5923        1151          2.6         386.7       1.0X
[info] cast(str as decimal) as c_decimal - with 1 spaces           3161           5838        1126          2.6         385.9       1.0X
[info] cast(str as decimal) as c_decimal - with 3 spaces           3046           3457         837          2.7         371.8       1.1X
[info] cast(str as decimal) as c_decimal - with 5 spaces           3053           4445         NaN          2.7         372.7       1.1X
[info]
```

Closes #26640 from yaooqinn/SPARK-30000.

Authored-by: Kent Yao <yaooqinn@hotmail.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>