For #26218
### Observations
The custom lint rules don't catch many issues. For example: this checks
for an illegal use of reader/writer in a function
(`containsIllegal(m["fn"]))`), but if the reader/writer code is
refactored into a different function, then this check will not fail.
Also, the rules lack tests, making them hard to maintain and potentially
irrelevant after code is refactored.
Carlo