Layout: Fix blockGap resolution for block style variations

[AtharvaSagane]

Currently, the layout engine ignores blockGap values defined within block style variations because it only checks block attributes and global styles. This PR updates gutenberg_render_layout_support_flag to resolve styles through WP_Theme_JSON_Resolver before falling back to global settings.

Testing Instructions:

Create a Block Style Variation for the Group block in theme.json that sets a specific blockGap (e.g., 0px).

Add a Group block to a page and apply this variation.

Verify in the frontend inspector that the child elements receive the variation's gap value instead of the global default.

[github-actions]

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Co-authored-by: AtharvaSagane <atharvasagane@git.wordpress.org>

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[github-actions]

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[AtharvaSagane]

Hi! This is my first PR. Could a maintainer please add the [Type] Bug and [Feature] Layout labels to this? Thank you!

[t-hamano]

Thanks for the PR!

Sorry, but since #74513 has already been submitted, I would like to close this PR.