[AggressiveInstCombine] Generalize foldGuardedRotateToFunnelShift to generic...

[AggressiveInstCombine] Generalize foldGuardedRotateToFunnelShift to generic funnel shifts (REAPPLIED)

The fold currently only handles rotation patterns, but with the maturation of backend funnel shift handling we can now realistically handle all funnel shift patterns.

This should allow us to begin resolving PR46896 et al.

Ensure we block poison in a funnel shift value - similar to rG0fe91ad4

Reapplied with fix for PR48068 - we weren't checking that the shift values could be hoisted from their basicblocks.

Differential Revision: https://reviews.llvm.org/D90625