[clang] [analyzer][NFC] Improve documentation of `invalidateRegion` methods (PR #102477)

[Balazs Benics via cfe-commits]

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

LGTM.
Do you plan to apply more refactors to invalidation and Store?
I'm asking because currently we experiment with a complete Store rewrite - touching there invalidation as well.

https://github.com/llvm/llvm-project/pull/102477