Split the routines to convert database fields to UUIDs into separate methods
Rename `updateDatabaseTables()` to `adjustDatabaseTables()`

The method will otherwise be called to early by the `runDatabaseUpdates()` method, which calls all methods starting with "update".
Enable the safe mode and maintenance mode during the database updates
Use `null` instead of `0` in `tl_files.pid`
Mark the backup database fields in the database updater
Merge branch 'hotfix/database-update' into release/3.2.0
Fix enabling the safe/maintenance mode during the version 2.9.2 update
Fix another phpDoc comment
Ignore the `database.sql` file if there is an `autoload.php` file
Replace `Config->getActiveModule()` with `ModuleLoader::getActive()`

This is just cosmetics, because the `Config` method is not deprecated.
Make sure the version 3.2 update is run even if the `tl_files.uuid` field exists
Add the PHP DOM extension to the system requirements
Correctly invalidate the cache of the local configuration file
Bypass the cache when checking for fields during the database update
Handle UUID strings in the UUID related `FilesModel` methods (see #6445)
Update the language files
Bump the version number