[clang-tools-extra] [clang-tidy] Clarify diagnostics of bugprone-sizeof-expression (PR #95550)

[Donát Nagy via cfe-commits]

NagyDonat wrote:

This commit is motivated by the discussion on https://github.com/llvm/llvm-project/pull/94356 .

Feel free to bikeshed the messages, I'm not too attached to the new choices, I'm just unsatisfied with the old ones.

https://github.com/llvm/llvm-project/pull/95550