[llvm] [AArch64] Refactor redundant PTEST optimisations (NFC) (PR #87802)

[Momchil Velikov via llvm-commits]

momchil-velikov wrote:

> What do you think to `canRemovePTestInstr` returning `std::optional<unsigned>`  ...

It'd be nicer, in principle, however this patch is extracting the NFC parts from https://github.com/llvm/llvm-project/pull/81141
where the pair becomes a tuple and gets one more member.


https://github.com/llvm/llvm-project/pull/87802