[FIR] Resolve rhs of += in dependent context

compiler/testData/diagnostics/tests/inference/genericAssignmentOperator.fir.kt

@@ -5,5 +5,5 @@ fun <T> f(): R<T> = R<T>()
 operator fun Int.plusAssign(y: R<Int>) {}
 
 fun box() {
-    <!INAPPLICABLE_CANDIDATE!>1 += f()<!>
+    1 += f()
 }

compiler/testData/diagnostics/tests/operatorsOverloading/kt1028.fir.kt

@@ -29,7 +29,7 @@ class Test()
     fun test()
     {
         val control = Control()
-        control.MouseMoved += { <!UNRESOLVED_REFERENCE!>it<!>.<!UNRESOLVED_REFERENCE!>X<!> } // here
+        control.MouseMoved += { it.X } // here
         control.MouseMoved.plusAssign( { it.X } ) // ok
     }
 }