JetDiagnosticsTest migrated to TestGenerator

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

compiler/testData/diagnostics/tests/regressions/kt307.kt

@@ -0,0 +1,11 @@
+// KT-307 Unresolved reference
+
+open class AL {
+    fun get(i : Int) : Any? = i
+}
+
+trait ALE<T> : AL {
+fun getOrNull(index: Int, value: T) : T {
+return get(index) as? T ?: value
+}
+}