XTVERSION support

[ryancdotorg]

This has been requested for other terminal emulators, e.g. vercel/hyper#5940 microsoft/terminal#18382

Since the TERM string is ambiguous, and feature probing is incomplete (for example, detecting 24 bit color support) it would be useful for xterm.js to identify itself in response to

CSI > q and CSI > 0 q

Looks like the relevant hooks in InputHandler.ts would look like

this._parser.registerCsiHandler({ prefix: '>', final: 'q' }, params => this.sendXtVersion(params));

public sendXtVersion(params: IParams): boolean {
    if (params.params[0] > 0) {
        return true;
    }

    this._coreService.triggerDataEvent(C0.ESC + `P>|xterm.js(${code to get version number goes here})`);

    return true;
}

The version number doesn't seem to be currently present in a way xterm.js can access it at runtime, so it would need to be injected somewhere as part of the build process.

[jerch]

@ryancdotorg Sadly it is not that easy for us to get a meaningful version string for xterm.js due to being highly configurable at different stages. Also see my comment here: microsoft/terminal#18382 (comment)