[llvm] [GISel] Funnel shift combiner port from SelectionDAG ISel to GlobalISel (PR #135132)

[Axel Sorenson via llvm-commits]

axelcool1234 wrote:

Now that the `hasOneUse` checks were determined to not be required, the original `lshr` and `shl` tests, which were converted into negative multi-use tests for funnel shifts, are no longer negative multi-use tests (they now trigger despite multiple uses of the intermediate instructions). Because of this, perhaps it'd be best to change these tests back to what they were before? I still have two new tests I've introduced that test `fshl` and `fshr`. 

Additionally, this file lacks vector versions of any of the shift tests. I'll look into introducing them.

https://github.com/llvm/llvm-project/pull/135132