Recommit "[RISCV] Use selectShiftMaskXLen ComplexPattern for isel of rotates."

Recommit "[RISCV] Use selectShiftMaskXLen ComplexPattern for isel of rotates."

This reverts commit dfe513ae1bb6e788ead93b850d80d77d54cf29d3.

Tests have been changed to avoid the type legalization bug being
fixed in D126036.

Original commit message:
This will remove masks on the shift amount. We usually get this with
SimplifyDemandedBits in DAGCombine, but that's restricted to cases
where the AND has a single use. selectShiftMaskXLen does not have
that restriction.