feat(ui): emit "msg_clear" event after clearing the screen (#34035)

Problem:  ext_messages cannot tell when the screen was cleared, which is
          needed to clear visible messages. An empty message is also
          never emitted, but clears messages from the message grid.
Solution: Repurpose the "msg_clear" event to be emitted when the screen
          was cleared. Emit an empty message with the `empty` kind to
          hint to a UI to clear the cmdline area.

0 files changed, 0 insertions, 0 deletions