Fix: support get activeElement in shadow DOM

[trinhnguyen-vn]

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Details

This pr is for fixing 2 problems

1. Component using document.activeElement cannot detect focused elements inside shadow roots, this break keyborad navigation and focus management in web component using shadow DOM. Affected component: MenuLlist, FocusTrap,...

Solution: create new utility getActiveElement: traverse shadow DOM recursively to find active element

Related issues: https://github.com/mui/material-ui/issues/34061 , https://github.com/mui/material-ui/issues/44147

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2. SSR runtime errror: getScrollbarSize utility throws error in SSR environment where window and document are undefined.

Solution: add defensive check in getScrollbarSize to handle undefined document/window

Issue details: