Convert TaskPrioritizer to kotlin.
Rename TaskPrioritizer.java -> .kt
Add variance test for nullable and function types.
Skip check variance for irrelevant classes
Create PRIVATE_TO_THIS visibility
Add serialization for PRIVATE_TO_THIS
Use Visibilities.isVisible with ReceiverValue.
Fix completion for private_to_this.
Delegated Properties: allowing type parameters for get/set methods

 #KT-6253 Fixed
Added test demonstrating usage of reified TP for dependency injection