FIR IDE: enable override implement test for FIR

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

@@ -0,0 +1,8 @@
+// ERROR: Unexpected token
+package foo
+
+class Impl: B {
+    override fun foo(r: Runnable!) {
+        <selection><caret>TODO("Not yet implemented")</selection>
+    }
+}