Checked that KT-4453 has been fixed recently by change in TipsManager
Completion: do not bold top-level functions
Completion: corrected presentation for extension properties
Completion: bold immediate members for extensions too
Removed code which does not seem to be needed at all
Added tests
Moved method checkIsExtensionCallable from ExpressionTypingUtils to TipsManager (converting it to Kottlin)
Moved methods for checking extensions applicability from TipsManager to extensionUtils.kt (and made them all extension methods)
Renamed TipsManager
Made ReferenceVariantsHelper class instead of object making method signatures shorter
Minor code refactorings
Buildserver auto merge