chore: fix types of component interface

[sscaff1]

Summary

The interface EditorComponentOptions does not match the documentation or usage. toPreview should be able to return a JSX.Element. Fields should be optional (for example, you create a component like a horizontal rule that would have no fields).

Test plan

This is just changing types.

Checklist

Please add a x inside each checkbox:

• I have read the contribution guidelines.

A picture of a cute animal (not mandatory but encouraged)

[martinjagodic]

Thanks!