[FIR] Fix resolution of LHS of augmented assignment operator call

Resolve it like a receiver of a call.
This makes the resolution result consistent with the equivalent
function call.

The K1 difference is covered by KT-66453.

#KT-66504 Fixed

compiler/testData/diagnostics/tests/resolve/operatorAndInfixResolve.fir.kt

@@ -59,7 +59,7 @@ fun test() {
     X()
 
     X.<!UNRESOLVED_REFERENCE!>plusAssign<!>("")
-    X += ""
+    X <!UNRESOLVED_REFERENCE!>+=<!> ""
     X<!NO_GET_METHOD!>[X]<!> += ""
 
     // Must resolve to property