JetDiagnosticsTest migrated to TestGenerator

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

compiler/testData/diagnostics/tests/inference/kt1293.kt

@@ -0,0 +1,11 @@
+//KT-1293 Kompiler doesn't show error when element of Array<Int?> is assigned to Int
+
+package kt1293
+
+fun main(args : Array<String>) {
+    val intArray = arrayOfNulls<Int>(10)
+    val <!UNUSED_VARIABLE!>i<!> : Int = <!TYPE_MISMATCH!>intArray[0]<!>
+    requiresInt(<!TYPE_MISMATCH!>intArray[0]<!>)
+}
+
+fun requiresInt(<!UNUSED_PARAMETER!>i<!>: Int) {}