formDialog doesn't have item hints and thus misses validation error messages

[e1fueg0]

Describe the bug:

dialog.formDialog looks very similar to widget.Form but, as the code is different, there's a difference:
widget.Form considers FormItem.HintText and creates helperOutput text widgets for items, and then it uses the helperOutputs to show validation errors if they occur.
dialog.NewForm uses its own code and thus it misses HintText and helperOutput, and thus validation error messages are missed.

To Reproduce:

Steps to reproduce the behaviour:

1. Run fyne_demo.
2. Go to Widgets/Form tab.
3. Enter aaaa to the Email field and click to another field.
4. The text Your full name will be replaced with not a valid email.
5. Go to Dialogs tab and click the Form Dialog button.
6. Try to reproduce the behavior there.

Device (please complete the following information):

• OS: Windows
• Version: 10
• Go version: 1.17.2, 1.18beta2
• Fyne version: 2.1.2

[andydotxyz]

I'm not sure this is quite accurate. The output for validation should be present if there is HintText or Validation set.
However it is indeed possible that the Form dialog gets this wrong, will need further consideration.

[andydotxyz]

Yeah, it looks like the Form dialog isn't re-using the Form widget code like it should and/or replicate the space reserved for validation errors.