Replace UNIX Sockets with XPC

[i2h3]

As discussed months ago internally in the desktop team, it would be beneficial in several ways to consolidate the interprocess communication between main app and extension(s). Currently, we also utilize UNIX socket files in addition to the standard XPC way.

• The UNIX sockets add unnecessary code to maintain the low-level implementation which we do not have with XPC
• The UNIX sockets are limited in their file path length which is a foreseeable problem with branded builds using long identifiers which will ultimately break them
• With XPC as the conventional first-party solution on the other hand we have unnecessary redundancy based on a different technology