[clang] [HLSL] Constant buffer layout struct update (PR #124840)

[Justin Bogner via cfe-commits]

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

This all looks reasonable, though it is kind of a mess of random fixes. It's generally best to commit unrelated things individually, and it would be nice to have commit messages that are full sentences of what and why rather than a bulleted list of various things that changed.

https://github.com/llvm/llvm-project/pull/124840