Minor in JS backend: added useful message to assert(for EA-48931) and drop unnecessary code.
JS backend: added tests for infix calls.

 #KT-3998   in progress
 #EA-56241 in progress
JS backend: fixed infix calls.

#KT-3998   fixed
#EA-56241 fixed
JS backend: fixed compiler crash when use compareTo in infix call.

#EA-54661 fixed