Steps to reproduce:

- Go to a website page > Add a 'Form' block > Add a new 'Selection'
field.
- Go to the page (in 'edit_translations' mode) > The selection field
options are not translatable.

The goal of this commit is to make the select options translatable
by adding an intermediate `.o_translation_select` element.

This element will handle option's text translations from the linked
`<select/>`. The final values are copied to the original element
right before save.

opw-3233360

closes odoo/odoo#117519

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