Added Binding.Delay feature

[TomEdwardsEnscape]

Updates to binding sources can now be delayed by configuring each binding.

What is the updated/expected behavior with this PR?

The delay feature works in the same way as WPF's. When the target property is changed, a DispatcherTimer is started (or restarted) and the source is only updated when the timer elapses.

As with WPF, there is no delay when the source is updated via UpdateSourceTrigger.LostFocus or BindingExpressionBase.UpdateSource(). Nor is there a delay when BindingMode.OneWayToSource is active and a new source object is provided.

Other binding types

MultiBinding does not support writing back to the source, so does not have a Delay property.

TemplateBinding could support Delay but I didn't implement it there. WPF's equivalent type doesn't have it, and I also don't see a use case within the context of a ControlTemplate.

Breaking changes

None

Obsoletions / Deprecations

None

Fixed issues

Fixes #7380

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0051473-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0051481-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[TomEdwardsEnscape]

Had to resolve a conflict here. In #17073 @grokys changed the line to:

WriteValueToSource(target.GetValue(TargetProperty));

But this skips the value equality check in WriteTargetValueToSource, which is used everywhere else. It looks a lot like this was an oversight, but perhaps there was a reason?

[avaloniaui-bot]

You can test this PR using the following package version. 11.3.999-cibuild0052802-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]