JBR-6325 Implement keyboard focus tracking for macOS Accessibility Zoom

[dmitrii-drobotov]

Next step after https://github.com/JetBrains/JetBrainsRuntime/pull/255, making the Accessibility Zoom follow keyboard focus changes.

• Call UAZoomChangeFocus function when the keyboard focus is changed or when an accessible selection event is fired. Zoom viewport fill follow the accessible frame of the newly focused component, and if it has selected children, their frame will be passed as part that needs to be highlighted.
• Fix an exception in ComboBoxAccessibility.accessibilitySelectedChildren when its selection is nil. This happens when a combo box doesn't have a selected item, and without this fix, Zoom wouldn't be able to follow the combo box location.
• Move the native handler of CAccessibility.focusChanged method from the legacy JavaComponentAccessibility to the new CommonComponentAccessibility class. It calls a class method (like a static method in Java), so there is no difference in which specific class it's located, but it allows to write the new code in the appropriate class.

Demo in IntelliJ and SwingSet: https://youtrack.jetbrains.com/issue/JBR-6325/macOS-No-keyboard-focus-tracking-while-using-Accessibility-Zoom-feature-with-IDE#focus=Comments-27-9125755.0-0.

[dmitrii-drobotov]

I also fixed a performance issue when selecting a lot of children, for example by pressing Cmd+A in a project tree or git log table with thousands of children. Calculating frames of all children caused long freezes in such cases, so I decided to use only the frame of the first selected child, which should be good enough in most cases.