[clang] [analyzer] Refine invalidation caused by `fread` (PR #93408)

[Donát Nagy via cfe-commits]

https://github.com/NagyDonat commented:

Thanks for publishing this commit, it's a nice refinement of the modelling capabilities, and mostly LGTM.

In the inline comments I added some very minor remarks and one question about the handling of a `fread` that reads into the beginning of an array region.

https://github.com/llvm/llvm-project/pull/93408