address reviews

Author: liufengyun

compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala

@@ -882,11 +882,13 @@ object messages {
 
   case class UncheckedTypePattern(msg: String)(implicit ctx: Context)
     extends Message(UncheckedTypePatternID) {
-    val kind = "Unchecked Type Pattern"
+    val kind = "Pattern Match Exhaustivity"
 
     val explanation =
       hl"""|Type arguments and type refinements are erased during compile time, thus it's
            |impossible to check them at run-time.
+           |
+           |You can either replace the type arguments by `_` or use `@unchecked`.
            |"""
   }