Summary:
This is mostly only moving the Sidebar from the old LayoutInspctor to a separate file. The old file was part of the UI component, however, it was super specific to the layout inspector, so I felt it makes sense moving it there.
Here is a diff between the new `src/plugins/layout/layout2/InspectorSidebar.js` and `src/ui/components/elements-inspector/sidebar.js`: P60951781
The old file is still kept around, as long as the old and new layout inspector are run side by side.
Reviewed By: passy
Differential Revision: D14100537
fbshipit-source-id: b5a6fbae9866732800bb9b2b8fb1b996b9861db6
649688db2a