KT-62138 add testcases

compiler/testData/diagnostics/tests/operatorsOverloading/plusAssignOnArray.kt

@@ -1,4 +1,3 @@
-// FIR_IDENTICAL
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
 class C {
@@ -13,9 +12,18 @@ class C1 {
     operator fun set(i: Int, v: C) {}
 }
 
+class C2 {
+    operator fun set(i: Int, v: C2) {}
+    operator fun get(i: Int): C2 = this
+}
+
+operator fun C2.plus(a: Any):C2 = this
+
 fun test() {
     val c = C()
     c[0] += ""
     var c1 = C1()
     c1[0] <!ASSIGN_OPERATOR_AMBIGUITY!>+=<!> ""
+    var c2 = C2()
+    c2<!NO_SET_METHOD!>[0]<!> += ""
 }