[llvm] [SLP] Vectorize full insertvalue buildvector sequences (PR #200274)

[Ryan Buchner via llvm-commits]

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bababuck wrote:

```suggestion
    case Instruction::InsertValue:
    case Instruction::InsertElement:
      Operands.assign(2, {VL.size(), nullptr});
      for (auto [Idx, V] : enumerate(VL)) {
        auto *IE = cast<Instruction>(V);
        for (auto [OpIdx, Ops] : enumerate(Operands))
          Ops[Idx] = IE->getOperand(OpIdx);
      }
      return;
```

https://github.com/llvm/llvm-project/pull/200274