feat(SplitButton): Add HotKey

[workgroupengineering]

Added HotKey property to SplitButton like Button and DropDownButton

What does the pull request do?

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

Obsoletions / Deprecations

Fixed issues

Fixes #14002

[avaloniaui-bot]

You can test this PR using the following package version. 11.1.999-cibuild0045040-beta. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[robloo]

Thanks! didn't have a chance to get to this one myself