Forms: Add filters to preload registration

[lezama]

Proposed changes:

• Add both path formats (with and without leading /) to preload data for compatibility with different apiFetch call patterns
• Add _locale=user variant of filters endpoint to cache both request types

What this PR does:

• Adds compatibility for API requests made with or without a leading / in the path (e.g., both wp/v2/feedback/filters and /wp/v2/feedback/filters)
• Includes the _locale=user variant of the filters endpoint to ensure requests with locale parameters are also cached

Note: This PR improves preload coverage but does not fully fix the middleware registration issue. A follow-up PR will be needed to change the script handle from self::SCRIPT_HANDLE to 'wp-api-fetch'
and position from 'before' to 'after' (these changes were reverted by the linter).

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

N/A - Performance optimization

Does this pull request change what data or activity we track or use?

No

Testing instructions:

• Open browser DevTools Network tab and filter for feedback requests
• Navigate to Jetpack → Forms → Inbox
• Verify no requests are made
• Check that the inbox loads correctly with form responses, filters, and counts displayed

Ref: #45339

[github-actions]

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[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WoA dev site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin (Jetpack), and enable the forms/fix-preload-middleware branch.
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bin/jetpack-downloader test jetpack forms/fix-preload-middleware

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[jp-launch-control]

Code Coverage Summary

Coverage changed in 1 file.

File	Coverage	Δ%	Δ Uncovered
projects/packages/forms/src/dashboard/class-dashboard.php	23/113 (20.35%)	-0.56%	3 ❤️‍🩹

Full summary · PHP report · JS report

[simison]

Should we go through usage and make sure we're calling the filters API consistently with or without a trailing /?