[dialog][popover] Fix focus restoration when focused element is hidden with CSS

[atomiks]

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Fixes #3299. While conditional rendering was handled via .isConnected, display: none (e.g. React.Activity) was not.

https://stackblitz.com/edit/eldph4db-edlqv6im

[pkg-pr-new[bot]]

vite-css-base-ui-example

pnpm add https://pkg.pr.new/mui/base-ui/@base-ui-components/react@3313

pnpm add https://pkg.pr.new/mui/base-ui/@base-ui-components/utils@3313

commit: 5d4e415

[mui-bot]

Bundle size report

Bundle	Parsed size	Gzip size
@base-ui-components/react	🔺+114B(+0.03%)	🔺+18B(+0.01%)

Details of bundle changes

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