[llvm] [DirectX][NFC] Change usage pattern DXIL* to Dxil* in DXIL Emitter (PR #80778)

[Chris B via llvm-commits]

https://github.com/llvm-beanz requested changes to this pull request.

There are only 4 places in the DirectX backend where we spell it `Dxil` today. this makes our spelling of the name less consistent not more.

While I'm not in favor of changing this spelling, if we want to we can discuss it but we should change it everywhere, not just in some places because that makes things worse.

https://github.com/llvm/llvm-project/pull/80778