[llvm] [DirectX] Add `llvm.dx.resource.getdimensions.x` intrinsic and lowering to DXIL (PR #161753)

[Chris B via llvm-commits]

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llvm-beanz wrote:

Serious praise here: It is fantastic that we're keeping docs updated with this work! This both makes it easier as a reviewer to make sure the change is correct, and will make it easier for contributors coming into the project.

https://github.com/llvm/llvm-project/pull/161753