[llvm] [LegalizeTypes] Handle non byte-sized elt types when splitting INSERT/EXTRACT_VECTOR_ELT (PR #93357)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> So it seems to make more sense in-tree (given by what ValueTypes.td currently looks like) to make use of getRoundIntegerType here. Or alternatively we should do something slightly more complicated by trying to find a legal type for ISD::STORE. But I don't know if there already exist some helper for that or if we would need to invent it.
> 
> I'll try to update this PR to use getRoundIntegerType instead of the getStoreSizedIntegerVectorElementType. And then we will deal with it downstream, if we want special handling for types like i24.
>

getTypeToTransformTo?

https://github.com/llvm/llvm-project/pull/93357