[FIX] web_editor: consider all remaining DOM changes before save

When clicking on save, the saved HTML should be what the user currently
sees. Before this commit, there might be cases where clicking on save
actually triggers a DOM update which occurs too late for the change to
be considered for the save. In 15.0, this manifests for example with
the blog cover saving*: if the color is being changed with the
colorpicker and that the user does not close the colorpicker before
saving, the color change is not considered because the previewMode=false
update of the colorpicker is not received. With this commit, we ensure
that DOM updates which occur because of the click on the save button
are considered before saving.

* That bug is however due to two other issues which are being fixed with
  the PR at [1].

[1]: https://github.com/odoo/odoo/pull/79028



closes odoo/odoo#81732

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