[clang-tools-extra] [clang-tidy] add new check readability-enum-initial-value (PR #86129)

[Piotr Zegar via cfe-commits]

https://github.com/PiotrZSL approved this pull request.

For me looks fine (had to check how it behave when coma is in next line).
Some ideas for separate check or future options:
- enforce that enums are sorted by value
- enforce that enums are sorted by name
- enforce that there is no duplicated values (bugprone), not there is warning for implicit duplicate, but not explicit.

https://github.com/llvm/llvm-project/pull/86129