Split up LibraryContext (frontend code refactor)

[bradenmacdonald]

This is a small-ish frontend refactor that will make it easier to develop the other UX improvements in this epic.

We should split up LibraryContext because it's getting too big and messy. We can instead have LibraryContext, SidebarContext, and ComponentPickerContext.

This will clean up our tests a lot too. The SidebarContext, and ComponentPickerContext can both have defaults so they don't always have to be present in order to read their values. (e.g. isSidebarOpen can just be false in the default context, even if there's no SidebarContextProvider available)