Shorten extension activation time by not unnecessarily awaiting async tasks within ExtensionSingleActivationServices

_Originally posted by @DonJayamanne in https://github.com/microsoft/vscode-jupyter/pull/11572#discussion_r990499647_

    this blocks the loading of the extension, can this be done in the background, 
    all of the activate methods run when extension loads and we wait for all of them to complete.
    i would suggest using the IExtensionSync.... interface

I didn’t realize that there is an IExtensionSyncActivationService which doesn’t block (await for long running tasks), and should be used whenever possible.

[amunger]

Maybe a better title would be “Shorten extension activation time by not unnecessarily awaiting async tasks within ExtensionSingleActivationServices” ?

[rebornix]

This sounds backwards - by definition synchronous will block

The blocking I’m referring to is any await happen in ExtensionSingleActivationService#activate will block the whole extension to be activated. A synchronous task will do the same, but if you have an async task but you kick off in IExtensionSyncActivationService#activate, we at least make sure that it’s a fire-and-forget, instead of holding off the extension activation process.

If this code contains some async code and MUST be completed before all of the extension starts completely then use the async version of the interface. Async stuff could be like loading somethings from files or the like. If this code contains some async code and need not be completed before all of the extension starts completely then use the non-async (IExtensionSyncActivationService) version & do not await on the promises (this way the activation will not be avaiting on these promises).

What @DonJayamanne put here is very accurate and they are the rules we want to follow.

https://github.com/microsoft/vscode-jupyter/blob/main/src/kernels/jupyter/finder/universalRemoteKernelFinderController.ts#L57 is a good example, ideally the remote kernel finder is Push Model and register kernels when it finds remote uris, but currently it’s blocking the activation.