[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 #81141 where the pair becomes a tuple and gets one more member.

Actually ...
I'll have a second look into using `std::optional` as it results in better generated code ...

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