[clang] [NFC][analyzer][docs] Document MallocChecker's ownership attributes (PR #121759)

[Donát Nagy via cfe-commits]

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

LGTM, thanks for adding this documentation!

I added an inline suggestion that -- hopefully -- clarifies the differences between held and taken memory areas; but the original is also completely OK. Feel free to ignore or tweak my suggestion if you prefer.

https://github.com/llvm/llvm-project/pull/121759