[fix] Consider line attribs of plugins when building changesets
[fix] Consider line attribs of plugins when building changesets

When checking the places on text that are identical between content
before and after a changeset, we were considering only the standard
(Etherpad-core) attributes, and not taking into account attributes
created by the plugins. One consequence was that the '*' marker of lines
with line attribs were being kept, even when the new lines have
different line attribs. See #3118 for more details.

Fix #3118.

University-of-Potsdam-MM/etherpad-lite,KonradMil/etherpad-lite,rschiang/etherpad-lite,tiblu/etherpad-lite,aptivate/etherpad-lite,joequant/etherpad-lite,storytouch/etherpad-lite,tiblu/etherpad-lite,cloudfoundry-community/etherpad-lite-cf,tiblu/etherpad-lite,KonradMil/etherpad-lite,lpagliari/etherpad-lite,aptivate/etherpad-lite,rschiang/etherpad-lite,aptivate/etherpad-lite,aptivate/etherpad-lite,University-of-Potsdam-MM/etherpad-lite,storytouch/etherpad-lite,University-of-Potsdam-MM/etherpad-lite,cloudfoundry-community/etherpad-lite-cf,lpagliari/etherpad-lite,storytouch/etherpad-lite,ether/etherpad-lite,lpagliari/etherpad-lite,KonradMil/etherpad-lite,ether/etherpad-lite,ether/etherpad-lite,joequant/etherpad-lite,rschiang/etherpad-lite,joequant/etherpad-lite,joequant/etherpad-lite,tiblu/etherpad-lite,lpagliari/etherpad-lite,University-of-Potsdam-MM/etherpad-lite,cloudfoundry-community/etherpad-lite-cf,KonradMil/etherpad-lite,rschiang/etherpad-lite,cloudfoundry-community/etherpad-lite-cf