extract DataFlowInfo from when-condition + more tests for kt2146

compiler/testData/diagnostics/tests/nullabilityAndAutoCasts/kt2146.jet

@@ -1,9 +1,40 @@
 //KT-2146 Nullability casts in when.
 package kt2146
 
-fun f(s : Int?) : Int {
+fun f1(s: Int?): Int {
     return when (s) {
         null -> 3
-        else -> s // type mismatch
+        else -> s
+    }
+}
+
+fun f2(s: Int?): Int {
+    return when (s) {
+        is 4 -> s
+        is null -> <!TYPE_MISMATCH!>s<!>
+        else -> s
+    }
+}
+
+fun f3(s: Int?): Int {
+    return when (s) {
+        is Int -> s
+        else -> <!TYPE_MISMATCH!>s<!>
+    }
+}
+
+fun f4(s: Int?): Int {
+    return when {
+        s == 4 -> s
+        s == null -> <!TYPE_MISMATCH!>s<!>
+        else -> s
+    }
+}
+
+fun f5(s: Int?): Int {
+    return when (s) {
+        s!! -> s
+        s -> <!TYPE_MISMATCH!>s<!>
+        else -> 0
     }
 }