[clang] [llvm] [HLSL] Create HLSL legalization passes (PR #123811)

[Justin Bogner via cfe-commits]

bogner wrote:

Sharing the code here makes sense to me, however, this does make the pass run significantly earlier in the DXIL pipeline. That might be fine but we'll have to make sure we aren't creating dead functions in any of the other DXIL backend passes that might have been cleaned up by this so far.

https://github.com/llvm/llvm-project/pull/123811