[clang] [clang][analyzer] Add checker 'unix.cstring.MissingTerminatingZero' (PR #146664)

[Balázs Kéri via cfe-commits]

balazske wrote:

The two patches (#149106 and this) are a different solution for the problem. I started the other because it looks more difficult to make this checker work if memory invalidations happen, probably many cases should be handled to maintain the checker internal data. The other solution has different problems (possible use of many `ElementRegion`'s, no good ability to handle memory copy functions), a decision is needed which is better to continue.

https://github.com/llvm/llvm-project/pull/146664