[Monaco] Add monaco.editor.registerLinkOpener method to be able to intercept opening links from the editor

[spahnke]

Fixes microsoft/monaco-editor#3354

By default the Monaco editor opens links clicked in the editor in a new tab. As stated in my comment in the above issue this is a good thing! However, there are situations where you want to handle the links yourself. For example, we have types of links that should be opened in the same tab, and we have types of links that should use our own window open method that transfers some state to the new tab/window. Everything else should still use the default.

This PR addresses that need by providing a monaco.editor.registerLinkOpener function that can be used to intercept the openening of links from the embedded editor and handle them however the embedder wishes to. The function delegates to the IOpenerService and returns an IDisposable instance to unregister the handler again.

Monaco Playground Code:

const text = `function hello() {
	alert('Hello world!');
	// https://www.example.com
}`;

// Hover on each property to see its docs!
monaco.editor.create(document.getElementById("container"), {
	value: text,
	language: "javascript",
	automaticLayout: true,
});

monaco.editor.registerLinkOpener({
	open(resource) {
		// do something with the link
		console.log(`handled ${resource}`);
		return true;
	}
});