[all components] Add visually hidden close button support with improved modal focus trapping

[atomiks]

• I have followed (at least) the PR section of the contributing guide.

visuallyHidden is a prop for ergonomics for non-Tailwind use and isn't strictly required; Tailwind already has "sr-only"

Closes #2722
Closes #3693 (for modal popups with close buttons. finalFocus is the preferred way to restore focus somewhere when the trigger gets removed as the current method is quite disorienting to screen readers anyway.)

New close parts:

• Combobox.Close
• Menu.Close
• Select.Close

Focus trap:

• Popover now traps when modal and a close part is rendered
• Menu: now traps when modal and Menu.Close exists
• Select: now traps when modal and Select.Close exists
• Combobox + Autocomplete: now traps for "input-inside-popup" layout when modal and Combobox.Close exists

Relevant combobox demos updated to use the Close part at the end of the list to escape it

[pkg-pr-new]

• base-ui-tanstack-start

• vite-css-base-ui-example

  pnpm add https://pkg.pr.new/@base-ui/react@4084
  

  pnpm add https://pkg.pr.new/@base-ui/utils@4084
  

commit: 82fa23c

[mui-bot]

Bundle size report

Bundle	Parsed size	Gzip size
@base-ui/react	🔺+1.65KB(+0.36%)	🔺+522B(+0.36%)

Details of bundle changes

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