JetDiagnosticsTest migrated to TestGenerator

- test data files renamed from *.jet to *.kt

compiler/testData/diagnostics/tests/override/ExtendFunctionClass.kt

@@ -0,0 +1,9 @@
+package extendFunctionClass
+
+class <!ABSTRACT_MEMBER_NOT_IMPLEMENTED!>A<!> : Function1<Int, Int>() {
+
+}
+
+class B : Function1<Int, Int>() {
+    override fun invoke(p1 : Int) = p1
+}