[llvm] [RISCV] Rename operands used for branch and compressed jump targets. NFC (PR #133364)

[Sam Elliott via llvm-commits]

lenary wrote:

@MaskRay when you say "many strange aliases", can you clarify which ones you mean? I think quite a few were added to be compatible with gas, but I am not sure.

As for handling multiple forms with the same mnemonic more gracefully, there are a few things here I'm looking at. One is that we use `bool` in many places when `DiagonosticPredicate` might allow us better control of which error message to use when - though I note that AArch64 (the only user of that mechanism so far) has some differences of opinion on exactly what to do there. The alternative is to use the mechanism ARM supports of "multiple near miss" support. I do intend to look at both, but haven't got back to it, and improving any register error messages causes a lot of test churn which I'm trying to time reasonably carefully.

https://github.com/llvm/llvm-project/pull/133364