Fix compound assignment on arbitrary expression in LHS

(with a convention compound assignment operator defined).

compiler/testData/ir/irText/expressions/augmentedAssignmentWithExpression.kt

@@ -0,0 +1,21 @@
+class Host {
+    operator fun plusAssign(x: Int) {}
+
+    fun test1() {
+        this += 1
+    }
+}
+
+fun foo() = Host()
+
+fun Host.test2() {
+    this += 1
+}
+
+fun test3() {
+    foo() += 1
+}
+
+fun test4(a: () -> Host) {
+    a() += 1
+}