[FIR] fixed overridden symbols of "invoke" in KFunction

IR expects overridden symbols of "invoke" in KFunction to be "invoke"
in the corresponding Function classes.
Before this commit we don't set overriddenSymbol, now we do.

compiler/testData/codegen/box/callableReference/function/extensionFromTopLevelUnitOneStringArg.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 fun run(arg1: A, arg2: String, funRef:A.(String) -> Unit): Unit {
     return arg1.funRef(arg2)
 }