Refactor dape's REPL messaging

- Add dape--message and dape--warning for displaying logs, matching
  the interface of message and warning.
- Add dape--repl-insert and dape--repl-insert-error for inserting
  strings with and without error face.
- Remove recursive guard for REPL since process callbacks or timers
  should not run during REPL editing.
- Simplify error buffer barfing logic.
- Remove specialized face usage to streamline styling.
- Allow dape-evaluate-expression to be used by the REPL input sender.