xterm.js node target and serialize addon

[Tyriar]

Part of #116113
Fixes #127638

This builds on xtermjs/xterm.js#3212 to maintain an xterm.js instance no the pty host and use that to replay in the terminal.

The current situation can take ~300ms to replay a full cache of events. This will can be event worse when rendering is taken into account and depending on hardware. Extend that to say 3 busy terminals and that's a second slower reloading. This PR by contrast takes ~30ms to replay the viewport + 100 rows of scrollback.

The setup needed is to copy node_modules/xterm into node_modules/xterm-headless and then copy over the webpack build from xtermjs/xterm.js#3212 and adjust package.json and typings/xterm-headless.d.ts.

The serialize addon is currently inlined because the UMD build is not compatible with node due to the use of self.

Remaining work:

• Finish Create a node.js target for xterm.js xtermjs/xterm.js#3212
• Automate xterm-headless publishing
• Addons
  • Publish and use a headless version of the serialize addon Package the serialize addon for xterm-headless xtermjs/xterm.js#3411
  • Publish and use a headless version of the unicode11 addon Package the unicode addon for xterm-headless xtermjs/xterm.js#3410
• Create opt-in flag to enable
• Create a setting for amount of scrollback to restore
• Dependencies
  • Add xterm-headless to core dependencies
  • Add xterm-headless to remote dependencies
• Review serialize addon code and tests
  • Ensure alt buffer mode is serialized
  • Evaluate any other holes in the serialize addon
• Investigate extra resize events
  • This was the devtools being opened firing another one, plus different entries show up for the same call within microtasks - there is only one call

[Tyriar]

Moved remaining follow ups to #116113