[clang] [NFC][Static Analyzer] Rename and discuss about `NotNullConstraint` & `NotNullBufferConstraint` (PR #131374)

[Balázs Kéri via cfe-commits]

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

Rename looks good. According to the format check code should be reformatted. Do not forget to remove the "discuss" part from the commit title.

https://github.com/llvm/llvm-project/pull/131374