[clang] [clang][analyzer] Support `fputs` in the StreamChecker (PR #73335)

[Ben Shi via cfe-commits]

benshi001 wrote:

> I prefer to have the new test code with `StreamTesterChecker_make_feof_stream` in a new test function (with appropriate name like `write_after_eof_is_allowed`), to improve code maintainability (`fputc` and `fputs` can be in the same function).
> 
> In github PR's usually force push is not the good way to update the code (it makes difficult to follow what was updated compared to the previous code). It is better to add new commits for the changes. The final "squash and merge" will merge all into one commit.

I have added a new test `write_after_eof_is_allowed` as you mentioned. Thanks.

https://github.com/llvm/llvm-project/pull/73335