[X86][AVX] Add lowerVectorShuffleAsLanePermuteAndPermute for v4f64 shuffles…


[X86][AVX] Add lowerVectorShuffleAsLanePermuteAndPermute for v4f64 shuffles (PR39161)

Add shuffle lowering for the case where we can shuffle the lanes into place followed by an in-lane permute.

This is mainly for cases where we can have non-repeating permutes in each lane, but for now I've just enabled it for v4f64 unary shuffles to fix PR39161 - there is no test coverage for other shuffles that might benefit yet.

We now have several cross-lane shuffle lowering methods that all do something similar - I've looked at merging some of these (notably by making the repeated mask mechanism in lowerVectorShuffleByMerging128BitLanes optional), but there is a lot of assertions/assumptions in the way that makes this tricky - I ended up going for adding yet another relatively simple method instead.

Differential Revision: https://reviews.llvm.org/D53148