Update ErrorSchema type

[jcqvisser]

Reasons for making this change

The current ErrorSchema type-definition does not allow one to create an ErrorSchema as recommended in the documentation.

This fixes #3239.

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 run npm run test:update to update snapshots, if needed.
  • I've updated docs if needed
  • I've updated the changelog with a description of the PR
• I'm adding a new feature
  • I've updated the playground with an example use of the feature

[heath-freenome]

Interesting that changing the type is causing the tests to break.

[jcqvisser]

I'll say! Will try and find some time to check it out today...

[heath-freenome]

@jcqvisser I dug into this and it seems that it is relatively impossible to build a recursive type that works for both writing and reading the data. Since the bulk of the use cases in the code is reading, I will be providing a WritableErrorSchema class that supports building an ErrorSchema that can be converted into a readable one by the class. Stay tuned