[llvm] [MC] Use StringTable for MCSchedClassDesc names (PR #137012)

[Min-Yih Hsu via llvm-commits]

https://github.com/mshockwave commented:

Do you think it'll be a good idea to share a single StringTable for all the sched models under the same target, e.g. A single X86SchedClassNames instead of Znver3SchedClassNames, SkylakeSchedClassNames etc. Given the fact that they basically share the same set of names?

https://github.com/llvm/llvm-project/pull/137012