Revert client-side media processing plugin-only gate

[adamsilverstein]

Summary

Once we fork WordPress 7.1, I plan to re-introduce the client side media feature. This PR restores core support in the plugin code path.

• Reverts Gate client-side media processing as plugin-only #76700 which gated client-side media processing as plugin-only
• Re-enables client-side media processing for WordPress core, in preparation for the 7.1 branch

This reverts commit d259aab.

Test plan

• Verify client-side media processing works in both the plugin and core contexts
• Confirm the VIPS loader script module is enqueued without the IS_GUTENBERG_PLUGIN check
• Confirm lib/media/load.php no longer early-returns for non-plugin contexts

[github-actions]

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[github-actions]

Flaky tests detected in 93e4a66.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/26188534208
📝 Reported issues:

• [Flaky Test] Navigates the items list via UP/DOWN arrow keys #64334 in /test/e2e/specs/site-editor/dataviews-list-layout-keyboard.spec.js
• [Flaky Test] should allow user to add and remove multiple local font files #62862 in /test/e2e/specs/admin/font-library.spec.js

[adamsilverstein]

7.1 is now open for commits, see https://make.wordpress.org/core/2026/05/20/commence-operation-wp-7-1/

[adamsilverstein]

I'm planning to reintroduce Client-side media in core in WordPress/wordpress-develop#11324. Once I do that we can merge this PR.

[alecgeatches]

I think I'm seeing some failed tests from trunk related to this PR:

1) Media_Processing_Test::test_get_rest_index_should_return_additional_settings_can_upload_files
Failed asserting that an array does not have the key 'image_output_formats'.

The first trunk failed test run here: https://github.com/WordPress/gutenberg/actions/runs/26585389684/job/78330386114 from the same commit 0a801ac merged above.

[adamsilverstein]

I think I'm seeing some failed tests from trunk related to this PR:

1) Media_Processing_Test::test_get_rest_index_should_return_additional_settings_can_upload_files
Failed asserting that an array does not have the key 'image_output_formats'.

The first trunk failed test run here: https://github.com/WordPress/gutenberg/actions/runs/26585389684/job/78330386114 from the same commit 0a801ac merged above.

Thanks, I'll take a look.

[adamsilverstein]

@alecgeatches - see #78788 - we can disable or remove the tests for now.