Provide the ability to show popups without having to subclass Popup

[bijington]

Description of Change

This is primarily aimed at playing around but also with the aim of exposing the implementation to see what everything thinks.

Linked Issues

• Fixes #

PR Checklist

• Has a linked Issue, and the Issue has been approved(bug) or Championed (feature/proposal)
• Has tests (if omitted, state reason in description)
• Has samples (if omitted, state reason in description)
• Rebased on top of main at time of PR
• Changes adhere to coding standard
• Documentation created or updated: https://github.com/MicrosoftDocs/CommunityToolkit/pulls

Additional information

[ne0rrmatrix]

I have ended up rewriting at least 3 or 4 samples submitted as bugs using standard DI pattern because the code would crash in IOS 17.x. I wanted to verify the issues that were being reported. If I see a bunch of different reports I put extra effort in.

Simplifying implementation would be great. I am all for that.

[bijington]

There are currently a couple of breaking changes to the IPopupService that I think are still good but we should consider documenting them to aid developers upgrading:

await popupService.ShowPopupAsync<MockPageViewModel>(CancellationToken.None);

becomes

await popupService.ShowPopupAsync<MockPageViewModel>(token: CancellationToken.None);

await Assert.ThrowsAsync<TaskCanceledException>(() => popupService.ShowPopupAsync<MockPageViewModel>(viewModel => viewModel.HasLoaded = true, cts.Token));

becomes

await Assert.ThrowsAsync<TaskCanceledException>(() => popupService.ShowPopupAsync<MockPageViewModel>(viewModel => viewModel.HasLoaded = true, token: cts.Token));

It also involves removing the ability to supply a viewModel instance to the Show methods to remove the confusion we have seen around developers expecting the BindingContext to automatically be set. I am happy to move this into a separate PR if we think it if worthwhile?

[brminnick]

@bijington FYI - we now have a few merge conflicts on this PR after merging a bunch of Popup PRs today