Fix custom hit testing

[wieslawsoltes]

What does the pull request do?

Fixes custom hit-testing broken in #5923

What is the current behavior?

Custom hit testing when custom title bar is used not working.

What is the updated/expected behavior with this PR?

Fixes custom hit-testing.

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

Check for correct interface.

Checklist

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

Breaking changes

Obsoletions / Deprecations

Fixed issues

[grokys]

Still not sure this is right, and I've been unable to test it: the description says "Custom hit testing when custom title bar is used not working." but when I run ControlCatalog and go to "Dialogs -> Decorated Window" the custom title bar seems to work fine?

First of all how do I repro the problem in order to verify the fix?

[wieslawsoltes]

Still not sure this is right, and I've been unable to test it: the description says "Custom hit testing when custom title bar is used not working." but when I run ControlCatalog and go to "Dialogs -> Decorated Window" the custom title bar seems to work fine?

First of all how do I repro the problem in order to verify the fix?

@grokys repro:

1. Run ControlCatalog.NetCore
2. Got to Window Customizations page
3. Check Extend Client Area to Decorations and Prefer System Chrome
4. Try dragging window by titlebar

[grokys]

Ok, reverted the TransformedBounds change as I've checked and this PR fixes custom title bar hit-testing on the deferred renderer without it and it was already broken on the immediate renderer before #5923, so makes no difference there either.