[llvm] Add SD matchers and unit test coverage for ISD::VECTOR_SHUFFLE (PR #119592)

[Craig Topper via llvm-commits]

topperc wrote:

I think kind of think we should have separate m_Shuffle and m_Mask/m_SpecificMask like IR. That will allow more m_*Mask to be added in the future. For example, we may want one that takes a function_ref to do custom matching. The IR match function for m_Mask/m_SpecificMask takes an `ArrayRef<int> Mask` as its argument.

https://github.com/llvm/llvm-project/pull/119592