[docs] remove ErrorList from FormProps docs, fix bad theme imports

[nickgros]

Reasons for making this change

Fixes #3758 - ErrorList prop should have been removed when v5 was released

Fixes #3760

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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