Fix some issues on SelectingItemsControls when items or control changes visibility

[timunie]

What does the pull request do?

• Fixes an issue where ListBox doesn't scroll selected item into view after becoming visible
• Fixes an issue where ColorPicker gets out of sync with SelectedIndex @robloo please test the ColorPicker part if it makes sense to you.

What is the current behavior?

SelectingItemsControls with AlwaysSelected set can select invisible items by accident

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

ColorView API was changed by removing not needed protected void

Obsoletions / Deprecations

Fixed issues

Fixes #14718
Fixes #13736 (@robloo this should be the last issue to solve, so I'll close the rollup with this PR)
Fixes #19663

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[timunie]

@MrJul there is now one change that should not backport, but the fix itself can be backported
@robloo please review the ColorPicker changes. On ControlCatalog I can now set the SelectedIndex without issues.

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[robloo]

I left some comments on the code changes but overall looks really good. I will have to find the time to test this later though. I've only looked at the code.

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[MrJul]

I've added several new failing tests for AlwaysSelected mode, related to the changes in this PR, and fixed them.
We should now be good to go.

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