[clang] [HLSL] Add NativeInt16Type langopt to control whether short type is supported. Enabled by default for all but HLSL. (PR #165584)

[Finn Plummer via cfe-commits]

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inbelic wrote:

We should also add a test (similar to [here](https://github.com/llvm/llvm-project/blob/main/clang/test/Driver/dxc_frs.hlsl)) that invokes `clang-dxc` with `-enable-16-bit-types` and `-###` to ensure that the flag is getting expanded as we expect

https://github.com/llvm/llvm-project/pull/165584