PatternMatchingTypingVisitor:

rewrite type inference for 'when' using special constructs.
This fixes several type inference issues for 'when':
KT-9929, KT-9972, KT-10439, KT-10463
along with some other diagnostics-related issues.

idea/testData/checker/infos/smartCastOnElvis.kt

@@ -1,15 +1,15 @@
 fun foo(s: String) = s.length
 
 fun baz(s: String?, r: String?): Int {
-    return foo(r <info descr="Smart cast to kotlin.String">?:</info> when {
-        s != null -> s
+    return foo(r ?: when {
+        s != null -> <info descr="Smart cast to kotlin.String">s</info>
         else -> ""
     })
 }
 
 fun bar(s: String?, r: String?): Int {
-    return (r <info descr="Smart cast to kotlin.String">?:</info> when {
-        s != null -> s
+    return (r ?: when {
+        s != null -> <info descr="Smart cast to kotlin.String">s</info>
         else -> ""
     }).length
 }