[llvm] [RISCV] Separate the analysis part of RISCVInsertVSETVLI. (PR #149574)

[Luke Lau via llvm-commits]

lukel97 wrote:

> Actually, nvm, sorry. For my purposes I don't really need to use this to see what VConfig reaches a particular instruction. I wil use RDA for that.
> 
> I do need the api which says which vconfig is compatible with given instruction

Does that mean we still need to split out the analysis pass from RISCVInsertVSETVLI? Do you have a rough draft to share of how this would look like plugged into #146971

https://github.com/llvm/llvm-project/pull/149574