FIR IDE: enable override implement test for FIR

idea/testData/codeInsight/overrideImplement/javaInterfaceMethod/foo/Impl.kt.fir.after

@@ -0,0 +1,7 @@
+import foo.Intf
+
+class Impl(): Intf {
+    override fun getFooBar(): String? {
+        <selection><caret>TODO("Not yet implemented")</selection>
+    }
+}