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

[Aidan Goldfarb via llvm-commits]

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@@ -226,6 +226,15 @@ inline SwitchContext<MatchContext, Pattern> m_Context(const MatchContext &Ctx,
   return SwitchContext<MatchContext, Pattern>{Ctx, std::move(P)};
 }
 
+struct m_Mask {
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AidanGoldfarb wrote:

As the capture logic is moved inside `SDShuffle_match`, I think removing this is correct.

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