fix: prevent content-gate editor.scss styles from getting chunked into the common.css file

[laurelfulford]

All Submissions:

• Have you followed the Newspack Contributing guideline?
• Does your code follow the WordPress' coding standards and VIP Go coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

This one was weird!

In #4646, a new file block-visibility.tsx started importing content-gate/editor.scss. Newspack Plugin's Webpack has minChunks: 2; since this was the second file editor.css was imported into, it started getting included in the common.css, which caused the .components-base-control styles in that CSS file to bleed into more post types.

The .components-base-control style wasn't very specific, but this only started being an issue when the styles were imported into more editors.

This PR does two things:

1. It moves the styles block-visiblity.tsx needed into its own CSS file, so editor.scss isn't being imported twice, and isn't getting added to the common.scss.
2. It makes the .components-base-control styles more specific (adding content gate-specific CSS classes) since this issue was still happening when you edited a Content Gate.

Closes NPPM-2812

How to test the changes in this Pull Request:

1. On trunk, edit a post and click the publish date in the sidebar; note the appearance of the date picker.
2. Apply this PR and run npm run build; refresh the post editor and confirm the date picker looks okay.
3. Using Woo Memberships, set up a Content Gate and confirm the same date picker looks okay.
4. Set up access control (add define( 'NEWSPACK_CONTENT_GATES', true ); to your wp-config.php, and set up a content gate).
5. Edit a post, and add a group block. Confirm the options in the 'Access Control' panel look okay.
6. Smoke test some of the other steps from feat(content-gate): add per-block access control for Group, Stack, and Row blocks #4646 and confirm things look okay.

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully ran tests with your changes locally?

[Copilot]

Pull request overview

This PR addresses unintended Gutenberg component styling bleed caused by editor.scss being imported by multiple entrypoints and ending up in a shared/common stylesheet chunk. It isolates the block visibility panel styles into a dedicated stylesheet and tweaks the generic BaseControl margin rule to avoid impacting the publish-date time UI.

Changes:

• Switched block-visibility.tsx to import a new block-visibility.scss instead of editor.scss, preventing editor.scss from being pulled into a common chunk.
• Extracted the block visibility panel SCSS from editor.scss into the new block-visibility.scss.
• Adjusted .components-base-control spacing in editor.scss to exclude DateTime/time-wrapper controls.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/content-gate/editor/editor.scss	Removes now-unneeded WP variables import, updates BaseControl margin behavior, and removes block-visibility panel styles (moved out).
src/content-gate/editor/block-visibility.tsx	Stops importing editor.scss and imports the new, dedicated block-visibility stylesheet.
src/content-gate/editor/block-visibility.scss	New isolated styles for the Access Control block visibility panel.

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