[FIX] web_editor: fix collapse opening on complex option hierarchy

When an option group is opened, all the other opened option groups were
closed. The problem is that an option group may contain other option
groups, so when trying to open a sub-group the main parent group was
closed first.

Note: this case only occurs for one option in themes for now.

Part of https://github.com/odoo/odoo/pull/38495
task-2083198