[FIX] web_editor: replace root style/class attrib

Issue

    - Install eLearning
    - Edit the header > change image
    - Save

    Image not changed

Cause

    We do not take new style/class attrib in account in
    replace_arch_section.

Solution

    Take them in account

OPW-2122947
OPW-2182109

closes odoo/odoo#44389

Signed-off-by: Jason Van Malder (jvm) <jvm@odoo.com>