Fix DateTimePickerPanelType enum backward compatibility

[rabbitism]

What does the pull request do?

The value (int) change of DateTimePickerPanelType.TimePeriod breaks backward compatibility. This PR brings it back.

What is the current behavior?

What is the updated/expected behavior with this PR?

How was the solution implemented (if it's not obvious)?

Checklist

• [ ] Added unit tests (if possible)?
• [ ] Added XML documentation to any related classes?
• [ ] Consider submitting a PR to https://github.com/AvaloniaUI/avalonia-docs with user documentation

Breaking changes

Well it breaks the breaking change.

Obsoletions / Deprecations

Fixed issues

[avaloniaui-bot]

You can test this PR using the following package version. 11.3.999-cibuild0052939-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[rabbitism]

@MrJul please help to review~

[MrJul]

For context: added in #16079 Didn't get caught by the API validation diff.