Introduce action to add missing when branches on sealed class

Made via diagnostics NON_EXHAUSTIVE_WHEN_FOR_SEALED_CLASS
with INFO severity and quick-fix
So #KT-17580 Fixed

idea/idea-analysis/src/org/jetbrains/kotlin/idea/highlighter/KotlinPsiChecker.kt

@@ -250,7 +250,7 @@ private class ElementAnnotator(private val element: PsiElement,
                         }
                 )
             }
-            Severity.INFO -> return // Do nothing
+            Severity.INFO -> AnnotationPresentationInfo(ranges, highlightType = ProblemHighlightType.INFORMATION)
         }
 
         setUpAnnotations(diagnostics, presentationInfo)
@@ -298,7 +298,7 @@ private class AnnotationPresentationInfo(
                     holder.createWarningAnnotation(range, defaultMessage)
                 }
             }
-            else -> throw IllegalArgumentException("Only ERROR and WARNING diagnostics are supported")
+            Severity.INFO -> holder.createInfoAnnotation(range, defaultMessage)
         }
 
         annotation.tooltip = getMessage(diagnostic)