Refactor: create responsive previews in the form builder

[JoshuaHungDinh]

Resolves GIVE-268

Description

This pull request (PR) introduces enhancements to achieve a width-responsive preview in the form builder by removing the sidebars from their fixed positioning. This creates a more similar experience as the WP block editor.

Changes include: interface-interface-skeleton__content

• Set height to allow content to be scrolled
• Set overflow-y to allow content to scroll

.interface-interface-skeleton__body

• Hide overflow so entire body does not scroll

.givewp-next-gen-sidebar

• remove fixed positioning

Affects

The visual form builder sidebars

Visuals

https://github.com/impress-org/givewp/assets/75056371/e9903e49-b03f-4da5-a965-738c5cd7838a

Testing Instructions

• Toggle the sidebars on each form builder section'Build', 'Design' & 'Settings', the content section should expand and retract accordingly.
• Each sidebar should be scrollable.
• The preview content should be scrollable.

Pre-review Checklist

• [x] Acceptance criteria satisfied and marked in related issue
• [ ] Relevant @unreleased tags included in DocBlocks
• [ ] Includes unit tests
• [ ] Reviewed by the designer (if follows a design)
• [x] Self Review of code and UX completed