Co-authored-by: Scott Lahteine <thinkyhead@users.noreply.github.com>

Fix #10388

This was present in #9357 but lost

Fixes #7250

Allows the user to send text to the serial console in order to
communicate with a host - sending debuging information or action
commands, for example.  Text must begin with '//' and this is added if
it is not already present at the beginning of the string.

Followup to #6940