JetDiagnosticsTest migrated to TestGenerator

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

compiler/testData/diagnostics/tests/nullabilityAndAutoCasts/kt1680.kt

@@ -0,0 +1,14 @@
+//KT-1680 Warn if non-null variable is compared to null
+package kt1680
+
+fun foo() {
+    val x = 1
+    if (<!SENSELESS_COMPARISON!>x != null<!>) {} // <-- need a warning here!
+    if (<!SENSELESS_COMPARISON!>x == null<!>) {}
+    if (<!SENSELESS_COMPARISON!>null != x<!>) {}
+    if (<!SENSELESS_COMPARISON!>null == x<!>) {}
+
+    val y : Int? = 1
+    if (y != null) {}
+    if (y == null) {}
+}