[clang] Remove experimental from Vector Crypto extensions (PR #69000)

[Alex Bradbury via cfe-commits]

asb wrote:

Thanks for the patch, some very quick feedback and I'd highlight the first bullet as the most important, as this is potentially a blocker for graduating these extensions from experimental.

* My big concern with this would be the intrinsics - could you please comment on the status of their standardisation?
* While doing this change, it would make sense to update the header of RISCVInstrInfoZvk.td. While it doesn't explicitly say it describes an experimental version of the extension, it references 1.0.0-rc1 of the spec while presumably there's now a 1.0.0-final?
* Please update llvm/docs/RISCVUsage.rst
* Please add a release note to llvm/docs/ReleaseNotes.rst

https://github.com/llvm/llvm-project/pull/69000