Auto merge of #143502 - scottmcm:aggregate-simd, r=oli-obk

Let `rvalue_creates_operand` return true for *all* `Rvalue::Aggregate`s

~~Draft for now because it's built on Ralf's rust-lang/rust#143291~~

Inspired by rust-lang/rust#138759 (comment) where I noticed that we were nearly at this point, plus the comments I was writing in rust-lang/rust#143410 that reminded me a type-dependent `true` is fine.

This PR splits the `OperandRef::builder` logic out to a separate type, with the updates needed to handle SIMD as well.  In doing so, that makes the existing `Aggregate` path in `codegen_rvalue_operand` capable of handing SIMD values just fine.

As a result, we no longer need to do layout calculations for aggregate result types when running the analysis to determine which things can be SSA in codegen.

Author: bors