Ability to use fullScreenCover rather than sheet for GalleryContent on iPad

[Pikuseru]

Checklist

• Reviewed the README and documents.
• Searched existing issues for ensure not duplicated.

Description

It'd be really nice to be able to view components using full screen cover on an iPad.

Motivation and Context

We're using Playbook to preview multiple components at a time (we're constructing pages made out of components), and sometimes our components are quite large and fill the whole screen. Apple's sheet presentation gives us quite a small preview area.

Proposed Solution

Giving us some way to configure the presentation, either as sheet or fullScreenCover, or replacing the modifier.

https://github.com/playbook-ui/playbook-ios/blob/master/Sources/PlaybookUI/Internal/Views/PlaybookGalleryContent.swift#L66