[clang] [clang][analyzer] Improve documentation of StreamChecker (NFC). (PR #83858)

[via cfe-commits]

================
@@ -3020,44 +3020,82 @@ Check for misuses of stream APIs. Check for misuses of stream APIs: ``fopen, fcl
 
 alpha.unix.Stream (C)
 """""""""""""""""""""
-Check stream handling functions: ``fopen, tmpfile, fclose, fread, fwrite, fseek, ftell, rewind, fgetpos,``
-``fsetpos, clearerr, feof, ferror, fileno``.
+Check C stream handling functions:
+``fopen, fdopen, freopen, tmpfile, fclose, fread, fwrite, fgetc, fgets, fputc, fputs, fprintf, fscanf, ungetc, getdelim, getline, fseek, fseeko, ftell, ftello, fflush, rewind, fgetpos, fsetpos, clearerr, feof, ferror, fileno``.
+
+The checker maintains information about the C stream objects (``FILE *``) and
+can detect error conditions related to use of streams. The following conditions
+are detected:
+
+* The ``FILE *`` pointer passed to the function is NULL. (At ``fflush``
+  NULL is allowed.)
+* Use of stream after close.
+* Opened stream is not closed.
+* Read from a stream after end-of-file. (This is not a fatal error but reported
+  by the checker. Stream remains in EOF state and the read operation fails.)
+* Use of stream when the file position is indeterminate after a previous failed
+  operation. Some functions are allowed in this state.
+* Invalid 3rd ("``whence``") argument to ``fseek``.
+
+The checker is not capable of maintaining a relation between integer file
----------------
NagyDonat wrote:

```suggestion
The checker does not track the correspondence between integer file
```
and re-apply line wrapping to the paragraph (if needed)

https://github.com/llvm/llvm-project/pull/83858