Fix HeadlessWindowImpl.Position does not persist new value

[loyvsc]

What does the pull request do?

Fixes #17071.

What is the current behavior?

When I assert the Position of the after I have set it, it always returns (0, 0).

What is the updated/expected behavior with this PR?

Now Position of the Window persist new value.

Breaking changes

Implementation of the HeadlessWindowImpl.Move method.

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0052032-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[cla-avalonia]

• All contributors have signed the CLA.

[maxkatz6]

Thanks!
Can you add a simple unit test for this?
For existing examples, see https://github.com/AvaloniaUI/Avalonia/tree/master/tests/Avalonia.Headless.UnitTests
These test source files are reused for two projects https://github.com/AvaloniaUI/Avalonia/tree/master/tests/Avalonia.Headless.NUnit.UnitTests and https://github.com/AvaloniaUI/Avalonia/tree/master/tests/Avalonia.Headless.XUnit.UnitTests

[loyvsc]

@cla-avalonia agree

[maxkatz6]

Thank you!

[maxkatz6]

Ah, approved before checking CI.
It seems like Should_Click_Button_On_Window test is failing.
Will restart, but should be double checked.

[MrJul]

The test failures are real.

The new test needs a Dispatcher.UIThread.RunJobs() at the end to run all jobs queued by Show() since it doesn't use any of the input methods that normally do this implicitly.

@maxkatz6 shouldn't we call RunJobs() automatically at the end of each test in the headless infrastructure, to make sure there's no pending jobs? I can PR that.

[maxkatz6]

@MrJul it would make sense, yes.

[MrJul]

Done for NUnit in #17140.
XUnit was already calling Dispatcher.RunJobs().

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0052209-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]