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

[David Peixotto via llvm-commits]

dmpots wrote:

> > > 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.
> > 
> > 
> > If we are sticking with the `DXIL` naming convention, then can we update this PR to catch all occurrences of the `Dxil` spelling? Or does this PR already cover that (not sure where the 4 instances occur).
> 
> The commit I pushed yesterday includes those 4 instances. They are in `DXILMetadata.cpp`. I checked to verify that there are no remaining occurrences of `Dxil` in the repo after the changes in this PR.

Ok, thanks for clarifying. LGTM.

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