Handle block quote like list item in editor

In the editor, if you are editing a list item and you git return, you get a new line that starts with a list item marker. Hit return again without typing further on the live and you get another new line and the item markers disappear.

I like this.

In contrast, if you're in a block quote, new lines will all have the indicator at their starts (`>`), no matter that the line had nothing in it.

I don't like this and suggest modifying the behavior of the editor in block quotes to match that in lists.

No source file or test is named in the issue. Start by locating the editor logic that continues list-item and block-quote markers after Return, then compare both behaviors. Done means a second Return on an empty block-quote line removes the quote marker as it does for list items.

Written by the indexing model from the issue text.