Theme: Skip serializing data-wpds-root-provider="false" on non-root providers

[ciampo]

What?

See #77462 (point I3).

Stops ThemeProvider from rendering data-wpds-root-provider="false" on every non-root provider.

Why?

The attribute is only ever matched as ="true" (by the prebuilt CSS and the runtime selector). Serializing "false" on every non-root provider is just dead markup.

How?

Set the attribute with data-wpds-root-provider={ isRoot || undefined } so React omits it entirely when isRoot is false.

Testing Instructions

1. Render a <ThemeProvider> without isRoot and confirm the wrapper <div> has no data-wpds-root-provider attribute.
2. Render a <ThemeProvider isRoot> and confirm the wrapper <div> still has data-wpds-root-provider="true".
3. Run npm run test:unit packages/theme.

Use of AI Tools

This PR was authored with the assistance of AI tooling (Cursor); all changes were reviewed by me.

[github-actions]

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Co-authored-by: ciampo <[email protected]>
Co-authored-by: mirka <[email protected]>

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[github-actions]

Size Change: +5 B (0%)

Total Size: 8.6 MB

📦 View Changed

Filename	Size	Change
build/scripts/theme/index.min.js	22.3 kB	+5 B (+0.02%)

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[mirka]

Straightforward 👍