[llvm] [LoongArch][Disassembler] Add symbolic operands for decoded immediates (PR #217971)

[Rong Mantle Bao via llvm-commits]

CSharperMantle wrote:

> [...] the LLVM community only allows squash commits [...]. This means that if you prefer to have your changes merged as separate commits, you will need to submit each commit as an individual PR. [...]

I don't really mind squashing. The separation of commits is purely for the convenience of review and patch organization, since I locally have multiple stacks in flight and rely on [megamerges](https://isaaccorbrey.com/notes/jujutsu-megamerges-for-fun-and-profit) to organize them. Please feel free to process them as you see fit.

https://github.com/llvm/llvm-project/pull/217971