Fix unindent action when acting on multiple list items

This is caused by a limitation of surface fragments in that they
always expand to include insertions touching them. In this case
we build surface fragments contain adjacent listItems, so when
the first listItem is de-listed a transaction is first created to
split the list. This insertion of ('/list', 'list') is adjacent
to the second surface fragment and so becomes part of that fragment.

This then causes the wrong node to be passed to unindentListItem.

The workaround is to use the inner range of the listItem, not
the outer range.

Bug: 48390

Change-Id: I7418910412d292ef4953e294a97f66e48d6f776f
Merge "Fix unindent action when acting on multiple list items"