Fix deadlock when VS is opended with GitHub pane visible

[jcansdale]

As a workaround for potential delays before await ThreadingHelper.SwitchToMainThreadAsync() returns, we changed to using await ThreadingHelper.MainThreadDispatcher.InvokeAsync(() => ...). Unfortunately rather than simply delays, this workaround can cause deadlock.

This PR:

• Revert back to using await ThreadingHelper.SwitchToMainThreadAsync()

These issues happen when Visual Studio is opened with the GitHub pane visible. It seems SwitchToMainThreadAsync doesn't return until the PR list has finished loading. 😨

We do need to find out what's causing this, but in a separate issue/PR. For the moment, let's get rid of the deadlock!

[shana]

If it's deadlocking, that means that the await for the InvokeAsync is happening on the main thread, that's the only thing I can think of that would cause a deadlock. Maybe it's possible that the InitializeAsync method is called on the main thread in some conditions. Can we repro the deadlock reliably? If we can, then maybe only doing the InvokeAsync if we're not on the main thread can solve this.

[jcansdale]

@shana @grokys,

It seems we need to use the following:

// `JoinableTaskFactory` is a property on `AsyncPackage`
await JoinableTaskFactory
   .WithPriority(VsTaskRunContext.UIThreadNormalPriority)
   .SwitchToMainThreadAsync();

I guess the default priority for extensions marked with AllowsBackgroundLoading = true must be UIThreadBackgroundPriority. This is too low for setting up UI elements like commands and the PR status bar element.

I'll follow up with another issue/PR.