This is a rather non-invasive change, that will
be easy to remove whenever we go ahead and stop
supporting older systems.

A WebKit processes should only be created when the user actually requests to open a file type requiring WebKit to be processed.

Commit adapted for atril, picked up from:
https://gitlab.gnome.org/GNOME/evince/-/commit/c3de8e75d6d0920478af210ba19a2d94b0734917

Credits to Benjamin Berg <bberg@redhat.com>

  | For large documents the linear search for the first link that is on a
  | certain page is really slow. Because of this scrolling becomes slow
  | whenever the page changes.
  |
  | Replace the linear search with a search in a binary tree populated with
  | the first link on each page and the corresponding GtkTreePath. This way
  | a specialized binary tree lookup can be used to find the closest
  | matching link and select that in the treeview.
  |
  | https://bugzilla.gnome.org/show_bug.cgi?id=779614