[llvm] [AArch64][GISel] Fold G_SHL used by multiple G_PTR_ADD into load/store addressing mode (PR #96603)

[David Green via llvm-commits]

davemgreen wrote:

See #86894 for how this should work. Some addressing modes are effectively free, so I don't believe it should matter of there are other uses. There are some target features that control what is considered free (as-in `FIXME: Consider checking HasAddrLSLSlow14 and HasALULSLFast as appropriate.`)

https://github.com/llvm/llvm-project/pull/96603