KT-2176 non-nullability is not inferred after !! or "as"

#KT-2176 Fixed

compiler/testData/diagnostics/tests/nullabilityAndAutoCasts/kt2176.jet

@@ -0,0 +1,27 @@
+//KT-2176 non-nullability is not inferred after !! or "as"
+package kt2176
+
+fun f1(a: String?) {
+    a!!
+    a: String
+}
+
+fun f2(a: String) {
+    a<!UNNECESSARY_NOT_NULL_ASSERTION!>!!<!>
+    a: String
+}
+
+fun f3(a: Any?) {
+    a as String
+    a: String
+}
+
+fun f4(a: Any) {
+    a as String
+    a: String
+}
+
+fun f5(a: String) {
+    a <!USELESS_CAST_STATIC_ASSERT_IS_FINE!>as<!> Any?
+    a: String
+}