Editor: Moving autobulleted line down causes duplicate `*` character

To repro:

1) Enter `* start a line like this on iOS`
2) Then put your cursor before the `*`, and press enter
3) it becomes `* * start a line like this on iOS`

I also run into this when I'm trying to copy and paste lists between each other, it's hard to put something in the middle.

Reproduce the iOS editor issue by entering the autobulleted line, placing the cursor before the asterisk, and pressing Enter; also check the copy-and-paste list case. Done means moving or inserting list content no longer creates a duplicate `*` character and the original list behavior remains intact.

Written by the indexing model from the issue text.