Inconsistency in "hint" binding usage in the informal API.

[kaladay]

Describe the bug
The expected behavior of the "hint" attribute and its binding is not clearly defined.
Different bindings are in use and this means that the expected "hint" behavior is inconsistent.

• validatedInputDirective.js
• validatedSelectDirective.js
• validatedTextAreaDirective.js (which previously had no hint and the binding is now arbitrarily selected.)

To Reproduce
Steps to reproduce the behavior:

1. Go to the links above.
2. View the bindings for hint.

Expected behavior
A consistent and defined expected behavior for "hint" and the appropriate binding to match the expected behavior.

The hint attribute on validated inputs of all types should act and behave with the same binding to avoid unexpected behavior, bugs, and regressions in projects utilizing weaver-ui-core.

Documentation of the expected bevavior should be also be provided to formalize the expected API behavior.