[iOS] Avoid setting embedding view controller background color

[GalaxiaGuy]

Description of Change

Changes the UIViewController created when embedding a Page on iOS to not explicitly set a background color (it was preventing embedding a transparent page).

Issues Resolved

• fixes [Bug] [iOS] It is not possible to embed a transparent Page natively with a transparent background  #13934

Platforms Affected

• iOS

Behavioral/Visual Changes

Pages that are transparent and embedded in iOS will now appear transparent.

Testing Procedure

An option has been added to the iOS embedding test bed to display a transparent page. This also contains some semi-transparent boxes. It is shown over a yellow background that should be visible.

Additionally, other pages should be unaffected.

PR Checklist

• Targets the correct branch
• Tests are passing (or failures are unrelated)

[GalaxiaGuy]

I'm planning on adding a test case to the embedding test bed project.

Is any more functionality needed? This would be a change in behavior if someone set a background color on a page with alpha and relied on there being white behind it when embedding. Which seems unlikely...

[GalaxiaGuy]

Platform.WillAppear sets the view's background color to ColorExtensions.BackgroundColor so the background color has to be set to Clear after that.

Is Platform.WillAppear only used for embedding? If so it may be better to make the change there.

[jfversluis]

Hey @GalaxiaGuy thanks for this one and thanks for your patience! I'm not going to last minute add this for the next service release, but I'll see about adding it to the next :)

[jfversluis]

Now that we're so close to the sunsetting of Xamarin.Forms unfortunately we won't be able to take this in anymore, we're really sorry about that. Nevertheless, thank you so much for your time and effort that you have put into this PR.

Please have a look at the evolution of Xamarin.Forms, .NET MAUI. A lot of development has been going on there. Hopefully this issue was already fixed in that codebase. If not, feel free to port this over to there.

Again, thank you so much for being a contributor and Xamarin.Forms user!