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

[Luke Lau via llvm-commits]

lukel97 wrote:

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

std::optional has equality defined on it so that `make_optional(x) == x`, I presume that's why the tests didn't need updated

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