[IMP] website_livechat, *: properly position the chatbox in edit mode

*: im_livechat

Also, fix its unopened position so that it stays at the same horizontal
position when opened.

task-2369225

closes odoo/odoo#61649

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>
Co-authored-by: qsm-odoo <qsm@odoo.com>