Add support for the VT answerback capability (#17660)

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

doc/cascadia/profiles.schema.json

@@ -3032,6 +3032,10 @@
           "description": "By default Windows treats Ctrl+Alt as an alias for AltGr. When altGrAliasing is set to false, this behavior will be disabled.",
           "type": "boolean"
         },
+        "answerbackMessage": {
+          "description": "The response that is sent when an ENQ control character is received.",
+          "type": "string"
+        },
         "source": {
           "description": "Stores the name of the profile generator that originated this profile.",
           "type": [