Support inheritance from java 8 interfaces

  #KT-5969 In Progress
Added inline annotation check on local funs
Obsolete KT-5685: VerifyError: Bad local variable type for class with inline method and optional parameters

 #KT-5685 Obsolete
Fix for KT-5995: Labeled val causes an exception from the back-end

  #KT-5995 Fixed
Generate labeled statements as statements
As designed KT-5930: Wrong execution order in case of extension function

  #KT-5930 As Designed
A flag in the JDR to govern usage of platform types
Flexible types added to JDR

So far they act exactly like inflexible ones
Fix compilation errors
Render flexible types in debug mode
Tests for Java method calls
Support flexible types in TypeCheckingProcedure
Minor. DelegatingFlexibleType moved to top level
TypeSubstitutor respects flexible types
Support flexible types in DataFlowValues
Fix the case of safe call and elvis operators: flexible types may be nullable
Test data fixed
Supertypes should not be flexible
Failing test isolated
Equality for flexible types