KT-2457 Verify error when comparing not null value with null in when

backend-side changes

compiler/testData/codegen/patternMatching/matchNotNullAgainstNullable.kt

@@ -0,0 +1,7 @@
+fun foo(i: Int, j: Int?): String =
+    when (i) {
+        j -> "OK"
+        else -> "Fail"
+    }
+
+fun box(): String = foo(0, 0)

compiler/testData/codegen/regressions/kt2457.kt

@@ -0,0 +1,8 @@
+fun foo(i: Int) : Int =
+    when (i) {
+        1 -> 1
+        null -> 1
+        else -> 1
+    }
+
+fun box() : String = if (foo(1) == 1) "OK" else "fail"