Added basic date/time picker automation peers.

[grokys]

What does the pull request do?

Currently, DatePicker and TimePicker have no automation peer, meaning that they don't show up in the automation tree¹.

This PR adds basic automation peers for these controls, causing them to show up as controls of type Custom in the automation tree. This matches how they show up in WPF (though in WinUI they show up as "Group" for some reason). UIA and NSAccessibility don't have a control type/role for date/time pickers.

The peers implement IValueProvider allowing the value to be set through automation. The parsing of the date/time is done using a simple DateTimeOffset.TryParse or TimeSpan.TryParse, so will use the OS/application culture.

Ideally, the automation peers should also implement IExpandCollapseProvider but this was not done here because:

• There is no IsDropDownOpen or equivalent API for opening/closing the date/time picker
• The date/time pickers in WinUI don't implement this provider either, so I doubt it's important

Footnotes

1. More accurately, they will show up only in the Raw view in UIA and isAccessibilityElement will return false on macOS ↩

[avaloniaui-bot]

You can test this PR using the following package version. 11.3.999-cibuild0053038-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[11khugener]

I did a quick tests if our application and automation now works.
Meaning automation id is now respected and we were able to set the value through IValueProvider.