[clang] [clang][analyzer] Add size constraints and summaries for POSIX I/O (PR #224980)

[Denys Fedoryshchenko via cfe-commits]

nuclearcat wrote:

Updating patch with the oversized-count warnings to be nonfatal so analysis can continue. Will add also regression tests for this behavior.

https://github.com/llvm/llvm-project/pull/224980