[IMP] web_editor: powerbox search from description

This commit changes web_editor's powerbox search feature to also look
for matches in a command's `description`, in addition to its `groupName`
and `title`.

For example, typing /track will suggest the Checklist command among the
suggestions as its description is "Track tasks with a checklist".

Note that only exact matches are considered for the description, while
fuzzy matches (with missing chars) work for other attributes.

Also fixes a typo in a local variable name because it was hazardous to
some people's eyesight.

task-3188758

closes odoo/odoo#113751

Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>