[llvm] [AArch64] Utilize `XAR` for certain vector rotates (PR #137629)

[Rajveer Singh Bharadwaj via llvm-commits]

Rajveer100 wrote:

I currently face this assertion:

```shell
Assertion failed: (*(AsmStrsvreg+RegAsmOffsetvreg[RegNo-1]) && "Invalid alt name index for register!"), function getRegisterName, file AArch64GenAsmWriter.inc, line 24199.
```

https://github.com/llvm/llvm-project/pull/137629