gplugin/gplugin

Make GPluginManager a final type

2021-10-12, Gary Kramlich
a1b0fd07c7f1
Make GPluginManager a final type

* Use g_signal_new_class_handler to handle the accumulator based signals
* Remove the optional struct offset for the non accumulator based signals
* This all fixes the warnings from vapigen as well

Testing Done:
Ran the unit tests, gplugin-query, and gplugin-gtk3-viewer without issue.

Reviewed at https://reviews.imfreedom.org/r/1028/
The following individuals have contributed to this project.
Ankit Vani <a@nevitus.org>
EionRobb <eion@robbmob.com>
Elliott Sales de Andrade <quantum.analyst@gmail.com>
Gary Kramlich <grim@reaperworld.com>
ivanhoe <ivanhoe@fiscari.de>
Jason Scherer <schereja@gmail.com>
John Bailey <rekkanoryo@rekkanoryo.org>
Mike Ruprecht <cmaiku@gmail.com>
Olaf Hering <olaf@aepfle.de>
Richard Laager <rlaager@pidgin.im>
Sorvival <sorvival@tutanota.com>