Extensions with a lot of xobjects became much slower to display when the content author is different from the metadata author

A fix in 16.3.0 and 15.10.9 caused the number of document clone to skyrocket (2 more for each extension page property display) when the content author is different from the metadata author (since it's a clone to hack the document content author to the metadata author without messing with the document in the cache, so we don't need to do anything when they are equals already).

Unfortunately, the clone can be very slow with documents containing xobjects with huge numbers (fixing this would probably be the fix for this issue too).

The workaround is to re-save the document with a modification in the content (to change the content author).