[VectorCombine] New folding pattern for extract/binop/shuffle chains (#145232)

Resolves #144654
Part of #143088

This adds a new `foldShuffleChainsToReduce` for horizontal reduction of
patterns like:

```llvm
define i16 @test_reduce_v8i16(<8 x i16> %a0) local_unnamed_addr #0 {
  %1 = shufflevector <8 x i16> %a0, <8 x i16> poison, <8 x i32> <i32 4, i32 5, i32 6, i32 7, i32 poison, i32 poison, i32 poison, i32 poison>
  %2 = tail call <8 x i16> @llvm.umin.v8i16(<8 x i16> %a0, <8 x i16> %1)
  %3 = shufflevector <8 x i16> %2, <8 x i16> poison, <8 x i32> <i32 2, i32 3, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
  %4 = tail call <8 x i16> @llvm.umin.v8i16(<8 x i16> %2, <8 x i16> %3)
  %5 = shufflevector <8 x i16> %4, <8 x i16> poison, <8 x i32> <i32 1, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
  %6 = tail call <8 x i16> @llvm.umin.v8i16(<8 x i16> %4, <8 x i16> %5)
  %7 = extractelement <8 x i16> %6, i64 0
  ret i16 %7
}
```
...which can be reduced to a llvm.vector.reduce.umin.v8i16(%a0)
intrinsic call.

Similar transformation for other ops when costs permit to do so.

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