Relax rules about inferring to Nothing for special calls

#KT-37388 Fixed
 #KT-38427 Fixed
 #KT-39953 Fixed
 #KT-38899 Fixed

compiler/testData/diagnostics/tests/smartCasts/publicVals/delegate.kt

@@ -14,7 +14,7 @@ class Example {
 
     public fun foo(): String {
         // Smart cast is not possible if property is delegated
-        return <!NI;TYPE_MISMATCH!>if (p != null) <!NI;SMARTCAST_IMPOSSIBLE, SMARTCAST_IMPOSSIBLE!>p<!> else ""<!>
+        return if (p != null) <!SMARTCAST_IMPOSSIBLE!>p<!> else ""
     }
 
     public fun bar(): String {