JetDiagnosticsTest migrated to TestGenerator

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

compiler/testData/diagnostics/tests/nullabilityAndAutoCasts/kt1270.kt

@@ -0,0 +1,12 @@
+//KT-1270 Poor highlighting when trying to dereference a nullable reference
+
+package kt1270
+
+fun foo() {
+    val sc = java.util.HashMap<String, SomeClass>()[""]
+    val <!UNUSED_VARIABLE!>value<!> = sc<!UNSAFE_CALL!>.<!>value
+}
+
+private class SomeClass() {
+    val value : Int = 5
+}