JetDiagnosticsTest migrated to TestGenerator

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

compiler/testData/diagnostics/tests/controlFlowAnalysis/kt1156.kt

@@ -0,0 +1,7 @@
+//KT-1156 Throwing exception on the right side of elvis operator marks code unreachable
+
+
+fun foo(maybe: Int?) {
+    val i : Int = maybe ?: throw RuntimeException("No value")
+    System.out.println(i)
+}