Automating addon releases during xterm release

[Tyriar]

I was just writing up the v4 release notes and it occurred to me that we could automate the version bumping of addons (#2410) when a stable version changed. We could do this by identifying the changed files between the previous release tag (latest on npm) and HEAD, instead of just the commit that we do here:

xterm.js/bin/publish.js

Lines 111 to 117 in 26a09f0

	function getChangedFilesInCommit(commit) {
	const args = ['log', '-m', '-1', '--name-only', `--pretty=format:`, commit];
	const result = cp.spawnSync('git', args);
	const output = result.stdout.toString();
	const changedFiles = output.split('\n').filter(e => e.length > 0);
	return changedFiles;
	}

Then if files changed within the addon, do a new stable release. In order to keep to semver's breaking changes we could just assume any change to an addon is a breaking change with a previous version and bump major here.

[Tyriar]

Linked this to #1921

[Tyriar]

Closing for now, let's do this manually a little more until we automate