PDF ligatures not enabled as Apache FOP ligatures are not encoded correctly for copy/paste/search

[ronaldtse]

Originally from metanorma/metanorma-ogc#284

Ligatures are turned off since v1.37 (https://github.com/metanorma/mn2pdf/releases/tag/v1.37) as they cannot be copy/paste/searched.

Long story short, this is an Apache FOP issue with ligatures not being encoded properly (though displayed properly), and the only workaround right now is to disable ligatures.

The relevant Apache FOP bug report is this:
https://issues.apache.org/jira/browse/FOP-2701

These comments describe the problem and investigation of the original problem.

• (Urgent) PDF: ligature text is not copy/pastable metanorma-ogc#284 (comment)
• (Urgent) PDF: ligature text is not copy/pastable metanorma-ogc#284 (comment)
• (Urgent) PDF: ligature text is not copy/pastable metanorma-ogc#284 (comment)
• (Urgent) PDF: ligature text is not copy/pastable metanorma-ogc#284 (comment)

We will reinvestigate this after the Apache FOP issue is resolved (or when we have time to resolve the Apache FOP issue).