Take into account implicitly defined types when rendering labels for fields

[perrinjerome]

getSchemaType is clever enough to figure out that a schema with
properties or additionalProperties has type "object", even if the
type is not explicitly defined, but getDisplayLabel does not have the
same logic, which results in displaying the label twice in cases where
the schema was guessed to be object.

Using getSchemaType as well in getDisplayLabel bring consistent
behavior and the label is rendered only once in that case.

Reasons for making this change

fixes #2501

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 for the PR! Note that this should also fix issues with other implicitly defined types (such as {const: true}) and properly display labels in those cases as well.