[toolbar] Set `disabled` attr on toolbar button when `focusableWhenDisabled={false}`

[mj12albert]

Preview: https://codesandbox.io/p/sandbox/priceless-einstein-w2qtyj

Fixes https://github.com/mui/base-ui/issues/2175

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

[mui-bot]

Bundle size report

Bundle	Parsed Size	Gzip Size
@base-ui-components/react	🔺+21B(+0.01%)	🔺+16B(+0.02%)

Details of bundle changes

Generated by :no_entry_sign: dangerJS against 309d9787413216a48d5b450035d868d6b3d2cf21

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commit: 309d978

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