Summary:
A feature that allows minimizing widgets on the ViewLayout.
- Code in ViewLayout and Layout hasn't been changed. Only some methods or variables were made public, and some events are now triggered when a section is dragged.
- Widgets can be collapsed or expanded (added back to the main area)
- Collapsed widgets can be expanded and shown as a popup
- Collapsed widgets support drugging, reordering, and transferring between the main and collapsed areas.
Test Plan: New test
Reviewers: georgegevoian
Reviewed By: georgegevoian
Differential Revision: https://phab.getgrist.com/D3779
