[clang] [Clang][RISCV] Add assumptions to vsetvli/vsetvlimax (PR #79975)

[Yingwei Zheng via cfe-commits]

dtcxzyw wrote:

Can we implement this in `computeKnownBitsFromOperator/getRangeForIntrinsic`?
https://github.com/llvm/llvm-project/blob/b21e3282864c9f7ad656c64bc375f5869ef76d19/llvm/lib/Analysis/ValueTracking.cpp#L1578-L1584

https://github.com/llvm/llvm-project/pull/79975