Inconsistent name encoding between field and class?

https://github.com/lampepfl/dotty/pull/13797#discussion_r735730881

```
    ProblemFilters.exclude[MissingFieldProblem]("scala.runtime.stdLibPatches.language.3.1"),
    ProblemFilters.exclude[MissingClassProblem]("scala.runtime.stdLibPatches.language$3$u002E1$"),
```

Probably should be made consistent by using the encoded field name?  I.e. `3$u002E1`.