[FIR IDE] Fix resolving sugared compound operators (like +=, -=)

^KTIJ-21374 Fixed

analysis/analysis-api/testData/referenceResolve/PlusAssignByHand.kt

@@ -0,0 +1,13 @@
+// UNRESOLVED_REFERENCE
+package test
+
+interface Foo
+
+interface WithOperator {
+    operator fun plus(f: Foo): WithOperator
+}
+
+fun test(withOperator: WithOperator, foo: Foo) {
+    var variable = withOperator
+    variable <caret>= variable + foo
+}