When instantiating classes that extend `inplace_editable` we can
improve performance by passing persistent instances we already have,
rather than re-requesting them.
Add test coverage to relevant classes.
Implement UI elements for editing columns of a report, taking their
definitions from the selected datasource.
Co-authored-By: David Matamoros <davidmc@moodle.com>
Co-authored-By: Mikel Martín <mikel@moodle.com>
Paul Holden