Added semantic and debug highlighting in library sources.
Removed obsolete action disabling error highlighting.
Minor. Reused constant.
Minor. Made method @NotNull.
Minor. Renamed local variable.
Simplified code.
Not ignoring other properties in scope.

First one (almost randomly) was chosen instead of ambiguity.
Correctly resolving all references in library source.

Added test with stdlib.

Ignoring top-level members from library source to avoid ambiguity. Resolving classes from source when deserializing descriptors (for unification).
Removed duplicating method.
Renamed method.