[clang] [clang][analyzer] Add more notes to PointerSubChecker (PR #102432)

[Donát Nagy via cfe-commits]

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

The change LGTM, it makes these reports somewhat easier to understand.

However, note that I'll delete all array bounds checking logic from this checker when I'll bring `alpha.security.ArrayBoundsV2` out of alpha, because there is no reason to have several checkers that are looking for the same error type. (Also note that the logic in `ArrayBoundsV2` is more sophisticated and general than the logic of this checker.)

This means that you shouldn't work on improving this part of this checker, because your efforts will be wasted when this is removed.

https://github.com/llvm/llvm-project/pull/102432