[llvm] [WIP][SLP] Use costing to decide between Strided Loads and Compressed Loads (PR #226540)

[Ryan Buchner via llvm-commits]

bababuck wrote:

Thanks for the guidance, Updated to move the decision into `transformNodes`. Will need to rebase as we made a change to the RISCV costing model for strided loads.

https://github.com/llvm/llvm-project/pull/226540