Media: Remove required attribute from media uploader file input field

[t-hamano]

• Trac ticket: https://core.trac.wordpress.org/ticket/64305
• Alternatives to Media: only add required attribute to media_upload_form on media screen #10558
• Introduced by https://core.trac.wordpress.org/changeset/60449

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Summary

When the media upload form operates as a normal async uploader, the file input element with the required attribute is visually hidden. When a form submit is performed on a form element with this attribute, the following error is displayed in the browser console, and the form is not submitted:

An invalid form control with name='async-upload' is not focusable.

This issue affects all implementations that run the media_upload_form() function within a form element.

As a temporary workaround for 6.9, remove the required attribute from the file input element.

Testing Instructions

✅ or ⚠️ indicates that this PR will change the results.

Default Media Uploader

• Access http://localhost:8889/wp-admin/media-new.php
• Click the "browser uploader" link
• If JS is enabled: The Upload button should be disabled unless a file is attached.
• ⚠️ If JS is disabled: The form will be submitted without attaching a file, but validation will be performed on the server side, and the message "No file was uploaded." will be displayed. Since cases where JS is disabled are rare these days, I think this case is acceptable.

Legacy Media Uploader

• Access http://localhost:8889/wp-admin/media-upload.php
• Click the "browser uploader" link
• ⚠️ The form will be submitted without attaching a file, but validation will be performed on the server side, and the message "No file was uploaded." will be displayed. Since the legacy uploader will probably be used very little anymore, I think this case is acceptable.

Backward compatibility with third-party plugins

• Install and activate the Envira Gallery plugin
  
• Access http://localhost:8889/wp-admin/post-new.php?post_type=envira
• Click the Publish button
• ✅ You can save the post successfully.

[github-actions]

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[github-actions]

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Props wildworks, krupajnanda, yagniksangani.

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[kjnanda]

@t-hamano I have tested this PR and verified all these scenarios mentioned here.

• Default Media Uploader ✅
• Legacy Media Uploader ✅
• Backward compatibility with third-party plugin. Eg. Envira gallery ✅
• Also, did a quick round of regression testing for different scenarios like drag-and-drop images, image short-code, multi file upload functionality etc just to ensure everything else is working as expected. ✅

Please confirm if there is anything I have missed. 🙇🏻‍♀️

[yagniksangani]

@t-hamano, Thanks for the fix. I have tested this PR and verified all the mentioned scenarios.

✅ Default Media Uploader
✅ Legacy Media Uploader
✅ Backward compatibility with third-party (Checked with Envira gallery and Soliloquy Slider Plugins)

Just to confirm, will this issue fix be included in the WordPress 6.9 release?

[adamsilverstein]

Looks good!

[github-actions]

A commit was made that fixes the Trac ticket referenced in the description of this pull request.

SVN changeset: 61320
GitHub commit: 3423501

This PR will be closed, but please confirm the accuracy of this and reopen if there is more work to be done.