[clang] [Clang][diagnostics] Improve the diagnostics for chained comparisons (PR #129285)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

Thank you for working on this! I think we can make the diagnostic message a bit more clear while we're at it, WDYT?

https://github.com/llvm/llvm-project/pull/129285