Add ltr.css support for RTL-based multilingual sites

[asadister]

Summary

Adds support for loading ltr.css in RTL-based multilingual WordPress sites, mirroring the existing rtl.css behavior.

Details

• Introduces wp_style_add_data( $handle, 'ltr', 'replace' ) and 'suffix' modes
• Uses extra['ltr'] and _css_href() for consistent file resolution
• Applies style_loader_tag filter for extensibility
• Ensures compatibility with single-file enqueue behavior in WordPress Core

Trac ticket: https://core.trac.wordpress.org/ticket/64193

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This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[github-actions]

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[github-actions]

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Props asadister.

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[github-actions]

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[asadister]

Closing in favor of #10476, which includes updated unit tests and resolves coding standards issues.
Thanks for the initial feedback!