fix: allows dispatching keyborg:focusin on focusable shadow root

[andreisaperski]

Keyborg doesn't dispatch keyborg:focusin for shadow roots when they get focus. Web components - e.g. fluent-button from Fluent UI Web Components - don't get keyborg:focusin dispatched for them because of that. The proposed fix lets keyborg:focusin event be dispatched for focused shadow root.

When focus goes back from element in shadow DOM to focusable shadow root (Shift+Tab), there's no focusin event dispatched for shadow root. The second part of the fix calls onFocusIn from focusOutHandler if relatedTarget of blur event is shadow root and it contains target element in its shadow DOM.