Fields should support error levels for messages

[tepi]

Describe your motivation

For bindings in a binder, you can add validators which produce errors with ErrorLevel.INFO or ErrorLevel.WARNING. Despite the level set, binder calls setInvalid(true) (and sets error message and theme) for a field regardless of the error level. On the other hand, when the binder checks the validity of its bindings, only actual errors are considered.

Describe the solution you'd like

In the future it would be preferable to be able to set info/warning level messages to fields without abusing the isValid flag along with a theme. A field could even have an info message and a validation error message at the same time.

This PR has more discussion on the enhancement.