Several new functionalities are possible with this change: the most requested is that callers can now check whether a control has a required validator. Other uses include incrementally changing the validators set without doing an expensive operation to reset all validators.
Closes#13461.
PR Close#42838
If the validator is bound to be `null` then no validation occurs and
attribute is not added to DOM.
For every validator type different PR will be raised as discussed in
https://github.com/angular/angular/pull/42378.
Closes#42267.
PR Close#42565