[llvm] [RISCV] Keep same SEW/LMUL ratio if possible in forward transfer (PR #69788)

[Wang Pengcheng via llvm-commits]

wangpc-pp wrote:

Just curious about why `llvm/unittests/Target/RISCV/RISCVBaseInfoTest.cpp` is passed? Is `gtest` able to auto dereference `std::optional`?

https://github.com/llvm/llvm-project/pull/69788