[llvm] [AArch64][GlobalISel] Add an initial fast path for common legal operations (PR #216691)

[Cullen Rhodes via llvm-commits]

c-rhodes wrote:

flame graph of sqlite here that gives a more detailed breakdown of where time is being spent in legalizer
<img width="1200" height="1670" alt="sqlite before legalizer fastpath" src="https://github.com/user-attachments/assets/d845e9f2-d961-4a10-9217-b561897abc19" />

>From a compile-time perspective I dont think how the legalizer works with the predicates std::function's is ideal. `llvm::GISelCSEAnalysisWrapper::get` is also pretty significant, but I've looked at that before in #197000

https://github.com/llvm/llvm-project/pull/216691