Collapse metadata on any removal.

In ve.dm.Document.getMetadataReplace(), we used to only merge metadata
if the amount removed is larger than the amount inserted.  But this
could end up putting metadata in odd positions, for example if you
have Foo[[Category:Bar]]Baz and you delete 'ooBa' and replace it with
{image}xxx{/image}, then the category ends up inside the image.

We should always merge metadata when a segment is deleted, so that it
appears outside any new structure added.

There's a weird corner case here when a segment is removed but no
insertion is made: the removed metadata then needs to get glommed onto
the next element.  We extend the insert/replace metadata array
when this happens.

Bug: 53444
Bug: 53445
Change-Id: I51d55fb370b473273f9cf152fdd0f356377d4109
Merge "Collapse metadata on any removal."