BREAKING CHANGE
Previously, the controlsErrors getter of ControlGroup and ControlArray returned the errors of their direct children. This was confusing because the result did not include the errors of nested children (ControlGroup -> ControlGroup -> Control). Making controlsErrors to include such errors would require inventing some custom serialization format, which applications would have to understand.
Since controlsErrors was just a convenience method, and it was causing confusing, we are removing it. If you want to get the errors of the whole form serialized into a single object, you can manually traverse the form and accumulate the errors. This way you have more control over how the errors are serialized.
Closes#5102
7343ef04ae