[Lona Studio] Implement bottom pane hide/show

[Devin Abbott]

Summary

This button should hide/show the bottom section of the UI, but currently it does nothing!

Let's fix that. Some new users have been pretty confused by why the bottom hasn't been responding...

Proposed Implementation

When the activePanes change... https://github.com/airbnb/Lona/blob/9ee49dfbb9d3dce6309c90b93c51c6949cf4f214/studio/LonaStudio/Workspace/WorkspaceViewController.swift#L84

We currently ignore the bottom pane: https://github.com/airbnb/Lona/blob/9ee49dfbb9d3dce6309c90b93c51c6949cf4f214/studio/LonaStudio/Workspace/WorkspaceViewController.swift#L301

Instead, we need to hide/show the bottomItem in the ComponentEditorViewController: https://github.com/airbnb/Lona/blob/9ee49dfbb9d3dce6309c90b93c51c6949cf4f214/studio/LonaStudio/Workspace/ComponentEditorViewController.swift#L213-L216

The easiest way to do this is probably to expose the bottomItem as a public or internal variable of the ComponentEditorViewController, but this isn't a great approach, since then we're exposing implementation details to a parent view controller. If we make bottomItem a member variable, it should be private.

Instead, let's add a variable var utilitiesViewVisible: Bool (with a didSet block) to ComponentEditorViewController, which we can then update from the WorkspaceViewController. The WorkspaceViewController contains an instance of ComponentEditorViewController we can use: https://github.com/airbnb/Lona/blob/9ee49dfbb9d3dce6309c90b93c51c6949cf4f214/studio/LonaStudio/Workspace/WorkspaceViewController.swift#L127

We'll also need to add/copy something similar to setVisibility into ComponentEditorViewController to do the actual hiding/showing.
https://github.com/airbnb/Lona/blob/9ee49dfbb9d3dce6309c90b93c51c6949cf4f214/studio/LonaStudio/Workspace/WorkspaceViewController.swift#L305-L315

For bonus points, also update the splitter https://github.com/airbnb/Lona/blob/9ee49dfbb9d3dce6309c90b93c51c6949cf4f214/studio/LonaStudio/Workspace/ComponentEditorViewController.swift#L151 to have a thickness of 0 when the bottom pane is hidden: https://github.com/airbnb/Lona/blob/9ee49dfbb9d3dce6309c90b93c51c6949cf4f214/studio/LonaStudio/Workspace/SectionSplitter.swift#L22

I'd recommend starting by setting a breakpoint in activePanes so you can see how clicking the toolbar button updates this value and take it from there.

[Volodymyr Klymenko]

I'll take this issue.

[Mathieu Dutour]

This is fixed right?