Validators should return AbstractValidators with nodev12

[zannkukai]

Describe the issue
When the RERO-ILS-UI linting is running, some warnings are raised due to Validator classes

WARNING: 89:20   deprecation  group is deprecated: This API is not typesafe and can result in issues with Closure Compiler renaming.
Use the `FormBuilder#group` overload with `AbstractControlOptions` instead.
Note that `AbstractControlOptions` expects `validators` and `asyncValidators` to be valid
validators. If you have custom validators, make sure their validation function parameter is
`AbstractControl` and not a sub-class, such as `FormGroup`. These functions will be called with
an object of type `AbstractControl` and that cannot be automatically downcast to a subclass, so
TypeScript sees this as an error. For example, change the `(group: FormGroup) =>
ValidationErrors|null` signature to be `(group: AbstractControl) => ValidationErrors|null`.

We should change the signature for all validators