Explore delaying doing * activation extensions until initial activation events are finished

[joyceerhl]

Today extensions which are * activated are resolved alongside other eager activation events. Explore whether deferring discovering and activating * activated extensions until the initial eager events have settled leads to better performance (e.g. in vscode.dev/github).

[joyceerhl]

Notes from initial investigation

Initial activation events that we want to see settle before handling * and workspaceContains eager events include:

• onFileSystem:vscode-vfs
• onFileSystem:review

Eager activation happens here:

vscode/src/vs/workbench/api/common/extHostExtensionService.ts

Lines 621 to 636 in 891a9e5

	private _handleEagerExtensions(): Promise<void> {
	const starActivation = this._activateByEvent('*', true).then(undefined, (err) => {
	this._logService.error(err);
	});
	this._register(this._extHostWorkspace.onDidChangeWorkspace((e) => this._handleWorkspaceContainsEagerExtensions(e.added)));
	const folders = this._extHostWorkspace.workspace ? this._extHostWorkspace.workspace.folders : [];
	const workspaceContainsActivation = this._handleWorkspaceContainsEagerExtensions(folders);
	const eagerExtensionsActivation = Promise.all([starActivation, workspaceContainsActivation]).then(() => { });
	Promise.race([eagerExtensionsActivation, timeout(10000)]).then(() => {
	this._activateAllStartupFinished();
	});
	return eagerExtensionsActivation;
	}

Debugging opening microsoft/vscode using Remote Repositories on desktop, these are the activation events I see coming in before eager activation takes place:

• onFileSystem:file <-- this shouldn't show up in web
• onFileSystem:vscode-userdata
• onView:timeline 🤔 (this is unexpected because it fires even when the timeline view is collapsed)
• onFileSystem:vscode-vfs
• onLanguage:Log 🤔 (this is unexpected because there are no open editors at this point, is this extension output channels-related perhaps?)

After eager extension activation events are activated but before the explorer has resolved, I also see:

• onSearch:vscode-vfs via here 🤔 (this is unexpected because the search viewlet is not focused at this point)

(Note, when viewing a PR, the actual onFileSystem:review event doesn't fire till after Remote Repositories has activated, figured out that we're looking at a PR based on the workspaceFolder URI, and activated the GHPRI extension via executing github.api.preloadPullRequest. If we wanted onFileSystem:review to be an 'initial' activation event that gets prioritized over eager events, we would likely need a faster path for firing onFileSystem:review.)

At a high level, I'm thinking of queuing all extension activation requests in the extHostExtensionActivator, then ensuring that when we see an eager event like * or workspaceContains, we wait for all queued activation promises to complete before handling the eager event itself.