Dealing with infix calls in completion

 #KT-4846 Fixed
Infix calls supported in smart completion too
Moved an utility method
Fixed KT-3807 Wrong completion for class/trait with extesion function

 #KT-3807 Fixed
Fixed KT-5808 Code completion auto-popup does not appear after typing "?."

 #KT-5808 Fixed
No completion auto-popup after dot in float literal (but one test start to fail!)
KT-4027 No type name completion in an incomplete generic extension function declaration
KT-2940 No completion in the receiver type argument position

 #KT-4027 Fixed
 #KT-2940 Fixed
More correct completion testing + fixed small bug in keyword completion
No completion auto-popup in generic function and property name
Extract method
Minor code refactoring