[llvm] [mlir] [utils][TableGen] Clarify usage of ClauseVal, rename to EnumVal (PR #141761)

[Krzysztof Parzyszek via llvm-commits]

kparzysz wrote:

PR stack:
1. https://github.com/llvm/llvm-project/pull/141761 (this PR)
2. https://github.com/llvm/llvm-project/pull/141762
3. https://github.com/llvm/llvm-project/pull/141763
4. https://github.com/llvm/llvm-project/pull/141765
5. https://github.com/llvm/llvm-project/pull/141766

https://github.com/llvm/llvm-project/pull/141761