Makes sure that the correct file extension is attributed when importing
a file using the Google Drive repository based on the set configuration
values for the default import format settings.
Instead of using the file title when generating the source attribute,
we should be using only the name of the Google Drive file in order to
avoid having the original extension within the filename after the file
is imported and added into Moodle.
This introduces a new "controlled link" file type where the file is not
stored in Moodle - but Moodle will control the access permissions on the file.
Plugins can "freeze" a filearea which means Moodle will take ownership of all the remote
files of this type.
When accessing a file, if the "filebrowser" infomation indicates the current user can write to the file, they
will be granted temporary write access.
Part of MDL-58220
