The answerback feature allows for the user to define a message that the
terminal will transmit to the host whenever an `ENQ` (enquiry) control
character is received.
## Detailed Description of the Pull Request / Additional comments
In Windows Terminal, the message can be configured at the profile level
of the settings file, as a string property named `AnswerbackMessage`.
In ConHost, the message can be configured in the registry, again as a
string value with the name `AnswerbackMessage`.
## Validation Steps Performed
I've confirmed that the control is working as intended in both Windows
Terminal and ConHost using Vttest.
Closes#11946