* Append proper suffixes to 16-bit literals for GLSL

The GLSL output path wasn't putting suffixes on literals of 16-bit types, and that was leading to compilation errors in downstream `glslang`. This change adds the suffixes defined by `GL_EXT_shader_explicit_arithmetic_types`.

This change also wraps up 8-bit literals so that they are emitted as, e.g., `int8_t(1)` instead of just `1`, to make sure we don't have implicit conversions in the output GLSL that weren't implicit in the Slang IR. We similarly wrap floating-point special values like infinities in their desired types when the type is `float` (e.g., `double(1.0 / 0.0)` for a double-precision infinity).

Note: Standad IEEE 754 half-precision doesn't provide an encoding for infinite or not-a-number values, so it might be considered an error if we emit `half(1.0 / 0.0)` but there really isn't a significantly better alternative for us to emit.

* fixup