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

^KTIJ-21374 Fixed

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

@@ -0,0 +1,12 @@
+package test
+
+interface Foo
+
+interface WithOperator {
+    operator fun plus(f: Foo): WithOperator
+}
+
+fun test(withOperator: WithOperator, foo: Foo) {
+    var variable = withOperator
+    variable <caret>+= foo
+}