Fix incorrect CMS layout widths when bulk editing

[kinglozzer]

Description

The edit form is missing the necessary CSS class to ensure its width is consistent with other CMS sections.

Before:

After:

Manual testing steps

Bulk edit something. My edit form includes an UploadField, not sure if that's relevant in triggering this, but it's definitely more noticeable at smaller screen sizes.

Issues

• Inconsistent CMS widths #294

Pull request checklist

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  • See picking the right version
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[GuySartorelli]

Thanks for raising this!

Since this is a commercially supported module, and commercial support for CMS 4 is now in "security patches only" phase, I can't merge this against the branch it's currently targetting without @colymba saying they're okay with a patch release for the CMS 4 compatible versions.

The alternative would be to retarget this PR to 4.0.

[lekoala]

the edit handler is really broken at the moment see #308

for the layout specifically, it also needs fill-height

would be great to have a working feature for the current silverstripe version :)

[GuySartorelli]

Closing in favour of #308