Defer work in extension activation

[joyceerhl]

The GHPRI extension currently takes upwards of 300ms to activate on my machine and @Tyriar's. If we could improve when GHPRI gets activated #4046 we could avoid paying this cost frequently, but perhaps there is work that we can defer to reduce overall extension activation time.

[Tyriar]

I notice activate is actually an async function here so those numbers might not reflect what we're thinking:

https://github.com/microsoft/vscode-pull-request-github/blob/main/src/extension.ts#L225

I wonder what the time would be if this:

vscode-pull-request-github/src/extension.ts

Lines 244 to 255 in 8e6b32a

	await vscode.commands.executeCommand('setContext', 'openDiffOnClick', openDiff);
	// initialize resources
	Resource.initialize(context);
	Logger.debug('Creating API implementation.', 'Activation');
	const apiImpl = new GitApiImpl();
	const version = vscode.extensions.getExtension(EXTENSION_ID)!.packageJSON.version;
	telemetry = new ExperimentationTelemetry(new TelemetryReporter(EXTENSION_ID, version, ingestionKey));
	context.subscriptions.push(telemetry);
	await deferredActivate(context, apiImpl, showPRController);

Was:

vscode.commands.executeCommand('setContext', 'openDiffOnClick', openDiff).then(() => {
  ...
})

Also I'm guessing async extension activation does not block other extensions activating?

[alexr00]

Found some places to improve. I measured from the start of activation until we're ready to display the tree of a checked out PR.
2.2 s speed up on desktop, for a total time of about 7 s.
170 ms speed up on vscode.dev, for a total time of about 2 s.

GHPRI is much faster on vscode.dev compared to desktop already and it seems like a combination of node-fetch being slow to make the first fetch and shelling out to git.

[alexr00]

I don't see a great way to verify this. Marking as verified to remove from our endgame queries.