[FIX] website: trigger visibility with prefilled form input

Form fields can be prefilled since [1] and their visibility
conditionally linked to other fields since [2].
1. This commit ensures prepopulated fields trigger the conditional
visibility mechanism (A), including when said field is first hidden,
then conditionally displayed (B).
2. Until [3], with a chain of visibility conditions, when one of them
was "contains", "does not contain" or a date-related condition, a
traceback was raised (C). This commit corrects the fix from [3] to
prevent this behavior now that the reason has been identified.
3. Tests are also set up to enforce these fixes.

Steps to reproduce (A):
- Drop a form
- Make field A depend on field B being set
- Have field B be autopopulated from user mail
- Save and check the form: A won't be shown despite B being set
- Removing one letter or typing anything in the input B will trigger
the visibility of A.
- Expected result: B should immediately appear.

Steps to reproduce (B):
- Drop a form
- Make field A depend on field B being set
- Have field B be autopopulated and depend on field C being set
- Field C is empty by default
- Save: only field C is shown. Type a letter: field B appears, but not
field A.
- Expected result: both should appear.
Note: this bug only occurs when field A is before field B.

Steps to reproduce (C) (until [3]):
- Drop a form
- Field A depends on B containing "abc"
- Field B depends on C being set
- Save and type something in C: there is a traceback.

task-3335536

[1]: https://github.com/odoo/odoo/commit/54873d2
[2]: https://github.com/odoo/odoo/commit/2dcbfec
[3]: https://github.com/odoo/odoo/commit/2714469



closes odoo/odoo#122044

Signed-off-by: Benoit Socias (bso) <bso@odoo.com>