DelegationSpecifier resolve depends on expected type (supertype)
Changed file extension to '.kt'
 to preserve file history
Converted ConstraintSystem to Kotlin
++Changed file extension to '.kt'
Added ConstraintPositionKind
 (to be able to filter by kind, not only by constraint position)

Rewritten ConstraintPosition in Kotlin
Small refactoring in ConstraintSystemImpl
Extracted isMyTypeVariable, getMyTypeVariable
todo: captured types
Removed ExpressionTypingContext.containingDeclaration
 it's always scope.getContainingDeclaration()
Introduced PackageReceiver instead of PackageType
Removed accidentally committed 'setTextRanges' from Diagnostic
Report 'nested class accessed via instance reference' error
Record reference to class object directly
not to containing class descriptor