[Form] Fixed expanded choice field to be marked invalid when unknown choices are submitted

#7939 must be merged before this PR is merged.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #5113, #5190
| License       | MIT
| Doc PR        | -

TODO:

- [x] test EntityChoiceList for stricter rules
- [ ] test ModelChoiceList for stricter rules
- [x] remove/deprecate the ChoiceList::getIndicesFor*() methods