[FIR-TEST] Add new testdata generated after changes in previous commit

compiler/testData/diagnostics/testsWithStdLib/kt8050.fir.kt

@@ -0,0 +1,11 @@
+private class X
+
+private operator fun X?.plus(p: Int) = X()
+
+class C {
+    private val map = hashMapOf<String, X>()
+
+    fun f() {
+        map[""] += 1
+    }
+}