JetDiagnosticsTest migrated to TestGenerator

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

compiler/testData/diagnostics/tests/nullabilityAndAutoCasts/kt2212.kt

@@ -0,0 +1,8 @@
+//KT-2212 Incomplete nullability information
+package kt2212
+
+fun main(args: Array<String>) {
+    val x: Int? = 1
+    if (x == null) return
+    System.out.println(x.plus(x<!UNNECESSARY_NOT_NULL_ASSERTION!>!!<!>))
+}