Post content does not have padding in the editor

[jffng]

Describe the bug

Currently because of where our padding is applied, post content does not appear with padding in the editor.

To Reproduce

1. Go to the post editor
2. Add some content
3. Preview on mobile

Expected behavior
I expect the padding to mirror what's displayed on the front-end.

Screenshots

Editor	Front-end

Additional context
This is happening because in our templates, we apply padding to a group block that contains the post-content, not the post-content itself or any children of it: https://github.com/WordPress/twentytwentytwo/blob/trunk/block-templates/single.html#L3

The editor only renders the post-content, which has no padding. It isn't aware of the container that has the padding applied, which I think is the correct behavior.

[kjellr]

Closing to consolidate this issue into #234.