[Metal][HLSL] Add support for dumping reflection (#185444)
The Metal Shader converter can output shader reflection information into
a JSON file. This connects the -Fre flag (DXC's flag for reflection) to
the Metal Shader Converter tool step to produce the JSON file. As a
temporary state the -Fre flag will error when used without the -metal
flag.
This is required to address
https://github.com/llvm/offload-test-suite/issues/452
Re-land #181258
