TODO(sll) in core/templates/services/validators.service.ts: Allow the warning to be more specific in terms of what needs to be entered.

[FaithAbiola]

The comment indicates that the warning message displayed when the isNonempty() function is called with an empty input should be more specific in terms of what the user needs to enter.

The task is to update the warning message to be more informative and helpful for the user.

[seanlip]

Closing as duplicate of #20336.