Notification of string changes

Author: Huong Nguyen
MDL-77576 core: Register new communication sub-system
Create a new subsystem for communication and create
associated experimental settings to safely use the
new subsystem.

Originally implemented as MDL-76699.

Co-Authored-By: Huong Nguyen <huongnv13@gmail.com>


http://git.moodle.org/gw?p=moodle.git;a=commit;h=163b4134df909044208adbbd8c3a05190f710a30
http://github.com/moodle/moodle/commit/163b4134df909044208adbbd8c3a05190f710a30

+ 4.3 en [enablecommunicationsubsystem,core_admin]
+ 4.3 en [enablecommunicationsubsystem_desc,core_admin]
+ 4.3 en [communication,communication]
+ 4.3 en [communicationprovidernotfound,communication]
+ 4.3 en [managecommunicationproviders,communication]
+ 4.3 en [nocommunicationprovider,communication]
+ 4.3 en [privacy:metadata,communication]