Add support for DA2 and DA3 device attributes reports

[j4james]

This PR adds support for the DA2 (Secondary Device Attributes) and
DA3 (Tertiary Device Attributes) escape sequences, which are standard
VT queries reporting basic information about the terminal.

The Secondary Device Attributes response is made up of a number of
parameters:

1. An identification code, for which I've used 0 to indicate that we
   have the capabilities of a VT100 (using code 0 for this is an XTerm
   convention, since technically DA2 would not have been supported by a
   VT100).
2. A firmware revision level, which some terminal emulators use to
   report their actual version number, but I thought it best we just
   hardcode a value of 10 (the DEC convention for 1.0).
3. Additional hardware options, which tend to be device specific, but
   I've followed the convention of the later DEC terminals using 1 to
   indicate the presence of a PC keyboard.

The Tertiary Device Attributes response was originally used to provide
a unique terminal identification code, and which some terminal emulators
use as a way to identify themselves. However, I think that's information
we'd probably prefer not to reveal, so I've followed the more common
practice of returning all zeros for the ID.

In terms of implementation, the only complication was the need to add an
additional code path in the OutputStateMachine to handle the > and
= intermediates (technically private parameter prefixes) that these
sequences require. I've done this as a single method - rather than one
for each prefix - since I think that makes the code easier to follow.

VALIDATION

I've added output engine tests to make sure the sequences are dispatched
correctly, and adapter tests to confirm that they are returning the
responses we expect. I've also manually confirmed that they pass the
Test of terminal reports in Vttest.

Closes #5836

[j4james]

For the record, I'm happy to consider returning a genuine version number in DA2 and some kind of ID in DA3 if that's preferable, but I thought we'd probably want to remain essentially anonymous. For more info on how these sequences are implemented and used, see issue #5836 (comment).

[DHowett]

So, it looks like xterm (344) responds to DA2 as a "VT420", firmware version "344", 0 (^[[>41;344;0c) in the default configu shipped with Debian buster.

I know that Vim, as an example, uses the xterm version, but I don't know if it uses DA2 or \e[>0q to do so.

For what it's worth, I can't get that build of xterm to respond to \e[>0q, and vim fails to autodetect it ... 😄 so I'm guessing it doesn't use DA2.

Regardless; how much should we pretend to be xterm and how much should we not? Open question!

[DHowett]

I do like the idea of remaining anonymous; I don't want people taking dependencies (like vim has done with xterm) on our implementation details especially when they change so rapidly in Terminal (and so slowly in Windows).
There's also no stable version number that we can use across Windows conhost and OpenConsole that would be monotonically increasing such that an application could rely on it.

[DHowett]

I see now that you literally covered everything I just said, in the comment I opened to "read after I wrote my comments". Sorry. 😬

[j4james]

Note that the \e[>0q sequence is a relative new thing. XTerm only added it in April (patch 354). I think it arose from discussions about standardising the TERM_PROGRAM and TERM_PROGRAM_VERSION environment variables (which is issue #1040 for us). But I'm in agreement with you that we're better off remaining anonymous and not supporting stuff like that until the app is more stable.

[DHowett]

I swear, you get fewer comments on your code reviews than the team does. I'm always impressed.

[miniksa]

Yep. Wonderful. I agree with the "remaining anonymous" policy for now. We can always revisit in the future if need be, but once a version system is out there, it's almost impossible to retract.

[ghost]

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[ghost]

🎉Windows Terminal Preview v1.2.2022.0 has been released which incorporates this pull request.:tada:

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