Internalize MessagingCenter

[jfversluis]

Description of Change

MessagingCenter was deprecated for net7, let's make it internal for net8 so we are free to remove/replace it whenever we want after that.

[jonathanpeppers]

It appears there is a memory leak every time you do:

await DisplayAlert("Done!", "Done!", "Ok");

maui/src/Controls/src/Core/Page.cs

Lines 239 to 244 in 918d1ce

	#pragma warning disable CS0618 // TODO: Remove when we internalize/replace MessagingCenter
	if (IsPlatformEnabled)
	MessagingCenter.Send(this, AlertSignalName, args);
	else
	_pendingActions.Add(() => MessagingCenter.Send(this, AlertSignalName, args));
	#pragma warning restore CS0618 // Type or member is obsolete

Is this a known issue with MessagingCenter?

[mattleibow]

That may have been one of the reasons we want to remove it. But probably we just want to reduce unnecessary complexity.

I got this one that needs my tests fixed #12910