[llvm] [AArch64][PAC] Introduce AArch64::PAC pseudo instruction (PR #146488)

[Daniil Kovalev via llvm-commits]

https://github.com/kovdan01 approved this pull request.

@atrosinenko Thanks for adding MIR tests for different MOVi{32|64}/MOVKXi patterns! This LGTM and I have no objections merging this.

https://github.com/llvm/llvm-project/pull/146488