Write full synthetic method signature for annotated property

This will be needed to support annotated extension properties, since they have
the same name but different signatures
Fix synthetic method generation for extension properties

If several annotated extension properties with the same name were declared in
one class, JVM issued a ClassFormatError, since we generated a synthetic method
for each of them with the same name and signature. Make the signature of this
synthetic method depend on a receiver parameter, if a property has one
Minor, extract test for synthetic methods for properties
Minor, extract method in CodegenTestCase
Generate synthetic methods for annotated properties in TImpl classes

Traits themselves can't have these methods, since it'd be a weird public method
in an interface
Minor, group tests related to synthetic methods for properties
Gensynmet
Add jet.KotlinTraitImpl annotation

Similarly to jet.KotlinPackageFragment, will be used to mark "$$TImpl" classes
generated for implementations of trait's methods and annotations of trait's
properties
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