Adds 'Preparing page display' progress bars for user interface pages
if they take a long time to display.
Also adds changes where other parts of the backup progress timed out on
long backups. After this change, and MDL-41838, it is finally possible on
my dev server to successfully back up the 'XL' test course.
encode_backup_temp_info() and decode_backup_temp_info() have been
introduced to keep the info field encoding in one place.
Many locations used get_backup_ids_record() to obtain info, that
makes lots of calls to get_backup_ids_record() which can be slow.
We now complete all those inline by adding the info field to the query.
To reduce memory usage, all queries of that nature have been changed
to use get_recordset_*. gzcompress was introduced if available to minimize
traffic to/from the database and to decrease the memory required for caching.
The compression time is saved by the benefits in other places of having smaller data.
There were still some differences between the php code
used in the issue and the php code generated by the
xmldb editor for the template tables. This commit put
both 100% in sync.
When we import courses or duplicate activities, the deduplicating nature of
the file_storage system means that we don't actually have to include the
real files in the backup - just their metadata from the file table.
The restoration process needs to know not to expect files from the backup
phase so a flag is set in moodle_backup metadata.
Some modes of backup cannot be preloaded with general backup
settings because they may conflict with the definitions required/set
by the mode (for example, import backups are, by definition, without
users always, so we cannot apply one default in the opposite direction).
So, after the patch, current general_backup setting will be only applied
to general backups, import/hub modes won't be using any default and
automated backup defaults should be loaded here (TODO)
