Rendering of headless tests fail about avalonia HOT 2 OPEN

@djalan you need to run Dispatcher jobs first, and only then timer tick. As otherwise render thread won't have anything to render.

But either way, we have tests for rendering into a bitmap:

For this bug we definitely need a minimal repro, as it works for me.

Note, CaptureRenderedFrame used in our tests is just a handy extension on top of ForceRenderTimerTick:
https://github.com/AvaloniaUI/Avalonia/blob/master/src/Headless/Avalonia.Headless/HeadlessWindowExtensions.cs#L22-L24

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@maxkatz6 I changed my code and most of the clicks in my application work well by simply using:

Dispatcher.UIThread.RunJobs();
AvaloniaHeadlessPlatform.ForceRenderTimerTick();

On the other hand, I experience problems when we use IPageTransition like in the below image. I tried using my loop to sync over 30 times with 10_000_000 ticks, but I still can't land on the final frame when I click the next button.

I had success in other parts of my application by calling my loop 4-5 times and with 100_000 or 1_000_000 ticks, but this one below looks like a dead end.

On two rare occassions, but it is not a constant behavior, I had success looping 20x with 10_000_000 ticks. I was able to see half of page 2, but it does not happen all the time. Increasing the numbers can end up yielding less frames.

I was able to sync (with a few loop calls) another part of the application that uses page transition too. I will compare the classes tomorrow.

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