[FIX] website: correctly mark translatable attributes

Steps to reproduce:

- Go to a website page > Add a 'Form' block > Set an input "Placeholder"
value.
- Go to the page (in 'edit_translations' mode) > The translation of the
input "Placeholder" attribute doesn't mark the input as translated and
even after saving the translation, the input is still marked as
"to_translate".

The goal of this commit is to fix this issue by extending the same
behaviour on the translated `<select/>` options (using `.oe_translated`
class) and setting the right translation state on the input from the
linked attribute translation `<span/>`.

task-3323245

closes odoo/odoo#121440

X-original-commit: 8b522e5c
Signed-off-by: Benoit Socias (bso) <bso@odoo.com>