Editor sheet detents

[boscojwho]

Checklist

• I have read CONTRIBUTING.md
• I have described what this PR contains
• This PR addresses one or more open issues that were assigned to me:
  - New post composer destroys composed post without confirmation on down-swipe #602
  - User feedback: Want to read what they're responding to while create/editing.
• If this PR alters the UI, I have attached pictures/videos

Pull Request Information

About this Pull Request

This PR includes two UI changes to Post editor and Response editor when presented as sheets:

1. Adds .medium presentation detent, while allowing users to interact with the view behind it while in .medium detent.

• Note: Interaction with view behind is only available on iOS 16.4 or later.

2. Disable interactive dismissal when editor has content.

Additional Notes

Sheet initially presents at .medium detent before moving to .large on initial presentation:

• To immediately present sheet in .large, we should pass a selection binding to .presentationDetents(...), but doing so causes the content view to call into its body, resulting in visible lag when switching between detents.
• To workaround this animation hitch, we could move the detent binding into each of the composer views, but we would also need to move the sheet's NavigationStack into the composers view, as well, since .sheet(...) expects presentation detent modifiers to be applied on the root view.

Screenshots and Videos

Comment.editor.mov

post.editor.mov

[EricBAndrews]

Merging per 12hr principle