[SLP] Fix cost model w.r.t. operand properties

We allow the target to report different costs depending on properties of the operands; given this, we have to make sure we pass the right set of operands and account for the fact that different scalar instructions can have operands with different properties.

As a motivating example, consider a set of multiplies which each multiply by a constant (but not all the same constant). Most of the constants are power of two (but not all).

If the target doesn't have support for non-uniform constant immediates, this will likely require constant materialization and a non-uniform multiply. However, depending on the balance of target costs for constant scalar multiplies vs a single vector multiply, this might or might not be a profitable vectorization.

This ends up basically being a rewrite of the existing code. Normally, I'd scope the change more narrowly, but I kept noticing things which seemed highly suspicious, and none of the existing code appears to have any test coverage at all. I think this is a case where simply throwing out the existing code and starting from scratch is reasonable.

This is a follow on to Alexey's D126885, but also handles the arithmetic instruction case since the existing code appears to have the same problem.

Differential Revision: https://reviews.llvm.org/D132566