JetDiagnosticsTest migrated to TestGenerator

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

compiler/testData/diagnostics/tests/ValAndFunOverrideCompatibilityClash.kt

@@ -0,0 +1,9 @@
+
+class Foo1() : java.util.ArrayList<Int>()
+
+open class Bar() {
+    fun v() : Int  = 1
+    val v : Int = 1
+}
+
+class Barr() : Bar() {}