These two diagnostics are similar: both are reported on type references
to enum entries. But `IS_ENUM_TYPE` is reported if the type ref is an
operand of `is` operator. To pass along this contextual information, a
boolean is added to FirSpecificTypeResolverTransformer.
This commit introduces several different things, in particular:
- check type arguments in expressions
- new TypeArgumentList node to deal with diagnostic source
- ConeDiagnostic was moved to fir:cones
- ConeIntermediateDiagnostic to use in inference (?) without reporting
- detailed diagnostics on error type
Tianyu Geng