[llvm] [DirectX] Set module-level flag `LowPrecisionPresent` in DXIL Shader Flags Analysis (PR #129109)

[Sarah Spall via llvm-commits]

https://github.com/spall commented:

Code LGTM but I don't understand the test enough to comment on if that is sufficient.

https://github.com/llvm/llvm-project/pull/129109