Description of the new feature/enhancement

When the window is in an un-maximized state, Terminal snaps window resizes to the closest character, which makes sense -- this way, the terminal padding on all 4 edges is what it's set to in settings.json.
However, when the window is maximized or in fullscreen, Terminal's size depends on the size of the monitor, which means the padding is often mismatched. When this happens, Terminal preserves the top and left padding. This makes some graphical CLI programs look a bit odd:

It might be nice to have an option to make the left-right and top-bottom paddings equal in this situation, so that the terminal content is centred within the window rather than at the top left.

Proposed technical implementation details (optional)

Of course, the padding setting should still be used as a minimum padding, and I think it makes sense to have this as a per-profile option (it makes more sense when you're running full-screen CLI programs like weechat, than if you're just running a shell.)