Fix omitData for top level array

[Tonexus]

Reasons for making this change

Enabling omitData currently converts a top level array to an object. Now includes a check if the form's top level type is an array, and converts back to an array if necessary.

#1396

Checklist

• I'm updating documentation
  • I've checked the rendering of the Markdown text I've added
• I'm adding or updating code
  • I've added and/or updated tests
  • I've updated docs if needed
• I'm adding a new feature
  • I've updated the playground with an example use of the feature

[epicfaace]

Thanks @Tonexus ! Can you add a test?

[Tonexus]

Ok, added one test to make sure the top level array stays as an array.