[llvm] [RISCV] Migrate getConstant indexed insert/extract subvector to new API (PR #139111)

[Philip Reames via llvm-commits]

preames wrote:

> > Digging through the code, the type used for the index will be the integer of pointer width from DL. For typical RV32 and RV64 configurations the pointer will be of equal width to XLEN, but you could have a 32b pointer on an RV64 machine.
> 
> This isn't possible with the existing possible DataLayouts right?

This question was the entire reason for posting for review.  I didn't know for sure.  :)

https://github.com/llvm/llvm-project/pull/139111