[REF] web, *: remove patchMixin + imp utils.patch

* hr, hr_holidays, im_livechat, mail, snailmail, website,
  website_livechat

This commit removes `patchMixin` and improve `utils.patch`.
`utils.patch` now supports native classes and has a new parameter
used to patch class members.

`utils.patch` is now used everywhere `patchMixin` was and it must
be used to patch classes.

closes odoo/odoo#65967

Related: odoo/enterprise#16278
Signed-off-by: Géry Debongnie (ged) <ged@openerp.com>
Co-authored-by: ged-odoo <ged@odoo.com>