[llvm] [AArch64][GISel] Always fold G_SHL into addressing mode where possible, unless the subtarget has addr-lsl-slow-14 (PR #96603)

[Amara Emerson via llvm-commits]

https://github.com/aemerson approved this pull request.

Would be good to understand why we still have differences to SDAG in the tests at some point.

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