4e0b68b516
All other compiler plugins accept "pkg1.pkg2.Class1" classes notation
and correctly match against it
But Assignment plugin used `ClassId` on such qualified names and got
`ClassId("/pkg1.pkg2.Class1")` instead of `ClassId("pkg1/pkg2/Class1")`,
and that lead to unexpected problems
This commit fixes that by using `FqName` instead of `ClassId`
^KT-57406 Fixed