Add keyboard protocol support (the kitty one)

[WSLUser]

Description of the new feature/enhancement

Provide a keyboard protocol for reporting raw keyboard input, preferably the Kitty keyboard protocol but at the very least XTMODKey, which Xterm supports.

Also see https://gitlab.freedesktop.org/terminal-wg/specifications/-/issues/1

Proposed technical implementation details (optional)

[zadjii-msft]

Is there a particular gap that win32-input-mode (#4999) doesn't cover that you're hoping to address?

[WSLUser]

These are based on VT CSI which I think win32-input-mode wouldn't provide (as that's specifically for win32, not VT applications). It's technically the same, but different audience. Some popular editors do appear to make use of them already, so providing the support on the VT side would be nice.

Also most notably, notcurses has support for the kitty keyboard protocol and minimum support for XTMODKey (it'll likely be re-iterated as time permits).

Also see #4999 (comment), which is basically this particular request.

[WSLUser]

#11264 also would reveal the need for this, if we want to do independent things from conhost (which you seemed to have wanted from the your reply to the comment linked above).

[WSLUser]

I guess the best proposol would be to re-work the input mode so that the win32 input would convert to one of the 2 proposed keyboard protocols. Easier would be to simply have 2 different ones, but that's asking for bad code health and inefficiencies, when much of what's already there can likely be re-used.

[zadjii-msft]

Sure okay, so this is on the client read input side, not the terminal write input side. Just "add support for {whatever} VT Input mode". That's fine, just a little different encoding from the other VT input types we have. Thanks for helping clarify!