[llvm] [DirectX] Add DXILRemoveUnusedResources pass (PR #200965)

[Joshua Batista via llvm-commits]

https://github.com/bob80905 approved this pull request.

LGTM, only question I have:
Why do you use `opt -S -dxil-remove-unused-resources ` in the third test, but use 
`llc -stop-after=dxil-resource-access` in the other two tests? Wouldn't the other 2 also work with `opt`? I somewhat prefer opt since it directly tests the pass you made.

https://github.com/llvm/llvm-project/pull/200965