[FIX] web_editor, website: fix onFocus/onBlur flow + add test

The flow has been broken multiple times across the years. Let's add a
test in all stable versions.

For this 14.0 forward-port, the test comes with a fix which restores the
13.0 flow which we tried to change in 14.0... but only ended up broking
it. Indeed, with [1], the 13.0 was fixed. And, with [2], we tried to
simplify the flow... but the explanation given by the commit is just
wrong: the flow was just broken and the simplification that was to be
done in fact practically never occurs. The more the reason to add a
test, proving how the flow is working. The simplification may be done
someday but not sure it is really worth it.

[1]: https://github.com/odoo/odoo/commit/076992bdf099f3a645c9a1ef6df2cdcccbf1c2b2
[2]: https://github.com/odoo/odoo/commit/5c007305c9998ade32c6677cac5552101c3a96af



closes odoo/odoo#79628

X-original-commit: dfb0ce4b
Signed-off-by: Romain Derie (rde) <rde@odoo.com>