feat: exposing findSchemaDefinition out of the utils lib

[erunion]

Reasons for making this change

Working on some resolving some bugs in a custom SchemaField that we've got, and I needed access to this so I could parse a $ref. Couldn't use it because it wasn't being exposed!

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, that does seem to be a useful util to export.

Still thinking about whether we should actually export utils from the same path / package though -- see #1642 (comment) -- but that's a discussion fro later.