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/SmartCastOnWhen.kt

@@ -1,7 +1,7 @@
 fun baz(s: String?): Int {
     if (s == null) return 0
-    return <info descr="Smart cast to kotlin.String">when</info>(<info descr="Smart cast to kotlin.String">s</info>) {
-        "abc" -> s
+    return when(<info descr="Smart cast to kotlin.String">s</info>) {
+        "abc" -> <info descr="Smart cast to kotlin.String">s</info>
         else -> "xyz"
     }.length
 }