AppBarSeparator / CommandBarSeparator should Derive from Separator #21015
Description
Describe the bug
Should not derive directly from TemplatedControl. Instead, it should derive from Separator.
https://github.com/AvaloniaUI/Avalonia/blob/master/src/Avalonia.Controls/Separator.cs
To Reproduce
See new control code referenced above.
Expected behavior
A separator should have the same base class.
Avalonia version
12.0 rc1
OS
No response
Additional context
No response