Fix leak/exception and links becoming bricked within the terminal

[Tyriar]

This PR fixes the long standing issue where links suddenly break in the terminal (#184046) as well as a few leak issues, one of which could trigger an exception which would likely cause other problems.

I reproduced the primary issue by using the following code on the exthost side to simulate an extension registering and disposing a single link provider:

let i = 0;
setInterval(() => {
	const id = ++i;
	console.log(`LINKS: register new (${id})`);
	const d = this.registerLinkProvider({
		handleTerminalLink(link) {
			return null!;
		},
		provideTerminalLinks(context, token) {
			return [];
		},
	});
	setTimeout(() => {
		console.log(`LINKS: dispose old (${id})`);
		d.dispose();
	}, 5000);
}, 10000);

This is why the issue was so hard to reproduce in OSS since it happened when extensions did something that was somewhat unexpected. After putting this in place it became clear that the problem was related to the clunky re-creation of TerminalLinkManager when the extension host disposes of all of its link providers here:

vscode/src/vs/workbench/contrib/terminalContrib/links/browser/terminal.links.contribution.ts

Lines 73 to 76 in ef40932

	this.add(this._terminalLinkProviderService.onDidRemoveLinkProvider(e => {
	linkManager.dispose();
	this.xtermReady(xterm);
	}));

Going deeper I found that xterm.js is holding onto disposed link adapters that were registered here:

vscode/src/vs/workbench/contrib/terminalContrib/links/browser/terminalLinkManager.ts

Line 351 in ef40932

this._linkProvidersDisposables.push(this._xterm.registerLinkProvider(p));

vscode/src/vs/workbench/contrib/terminalContrib/links/browser/terminalLinkManager.ts

Line 360 in ef40932

const newLinkProvider = this._xterm.registerLinkProvider(wrappedLinkProvider);

So that fix was a matter of correctly disposing them when the link manager was replaced.

The TerminalLinkManager disposal is still in place and I noticed that when that happens it causes links to disappear, so it could be related to another issue where link underlines flicker. This is deferred though as this PR is complicated enough and that would need a new upstream API.

Fixes #184046
Fixes #203437

[meganrogge]

👏🏼

[a8t]

omg thank you!!!