[FIX] web: restore dialog callback calls (e.g. cloning a website page)

Commit [1] broke some confirm dialogs because the confirm and cancel
callbacks are not called with the same `this` anymore.

E.g.:
- Install website
- Go to the page manager (/website/pages)
- Clone a page (choose a name and confirm)
=> Crash (this.$ does not exist).

Note that this flow was quickly fixed with [2] by changing the local
code instead of fixing the root cause (this commit here actually
technically reverts that change so it keeps working).

The work done at [1] actually needed some more rework than that to
handle two other potential usecases:

- If the confirm dialog handlers' promises are rejected, the dialog is
  not closed (rightfully, like for example allowing to fill an empty
  required input)... but [1] prevented to click on the button again
  forever. With the same example as above, it can be reproduced: if the
  RPC to clone the page fails, I cannot retry.

- If not both confirm_callback and cancel_callback were given, [1] only
  prevented to multi-click on the related button (e.g. if you click on
  "Ok", a RPC which takes 10 seconds is made, you click on cancel
  immediately afterwards -> the dialog is closed while it should be
  prevented (and would be if cancel_callback was given, following [1])).
  That may not be entirely stable to make this change though but it
  seems to make sense and be better (just keeping what [1] wanted here).

Note: this adds some more tests to check all of this + some more things
that were found during development. For example: [1] relied on the fact
that callbacks returned a Promise or nothing... while developers
actually were returning random things (for no reason as no way to get
the result anyway). Adding a test for this prevents to break that in
stable (the first iteration here crashed in such cases).

[1]: https://github.com/odoo/odoo/commit/4b8b079a7d9991a8dc481fe71a45185d672135c9
[2]: https://github.com/odoo/odoo/commit/8216341f5ad8d82ad0bcb0d1f01d874477d2de7b

Closes https://github.com/odoo/odoo/pull/103712


opw-3033878
opw-3043224
opw-3046485
opw-3042542

closes odoo/odoo#104220

Signed-off-by: Aaron Bohy (aab) <aab@odoo.com>