Cover Block: Enable fixed background support for videos

[saurabh-G07]

PR Description: Cover Block - Enable Fixed Background for Videos
Related Issue: #52585

Description

This Pull Request extends the "Fixed background" (parallax) functionality to the Cover block when a Video is selected as the background media. Previously, this feature was only available for Images.

Implementation Details

Unlike images, which utilize background-attachment: fixed on a container div, video elements (<video>) do not support this CSS property.

To achieve feature parity, this PR implements a solution using:

1. position: fixed on the <video> element to anchor it to the viewport.
2. clip-path: inset(0) on the parent .wp-block-cover container. This ensures the fixed video is correctly "clipped" to the block's area as the user scrolls, replicating the background-attachment behavior.

Changes

• inspector-controls.js: Updated the "Fixed background" toggle logic to be visible when isVideoBackground is true.
• save.js: Passed the has-parallax class to the <video> element when the attribute is set.
• style.scss: Added the necessary CSS rules for video.has-parallax (using position: fixed) and the container (using clip-path).

Testing Instructions

1. Insert a Cover Block.
2. Choose a Video from the media library.
3. Open the Block Settings sidebar.
4. Toggle "Fixed background" to ON.
5. Scroll the page and verify the video remains fixed relative to the viewport (parallax effect).
6. Verify that the "Repeated background" toggle remains hidden for videos (as it is not supported).

Checklist:

• My code is tested.
• My code follows the WordPress coding standards.
• I have added a unit test to verify the toggle state.
• I have verified the behavior on different viewports.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

[github-actions]

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[github-actions]

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[t-hamano]

Thanks for the PR!

Regarding this enhancement, #74289 has already been submitted, so let me close this PR.