Refactor: remove unnecessary indirectness in get default form state test

[x0k]

Reasons for making this change

In a recent release, excessive indirectness was added to the test, making it less readable and harder to extend.

I have regrouped the tests as follows:

• object schemas
  • [test case]
    • getDefaultFormState
    • computeDefaults
    • getDefaultBasedOnSchemaType
    • getObjectDefaults
    • (with additional options)
      • getDefaultFormState
      • computeDefaults
      • getDefaultBasedOnSchemaType
      • getObjectDefaults
• array schemas
  • [test case]
    • getDefaultFormState
    • computeDefaults
    • getDefaultBasedOnSchemaType
    • getArrayDefaults
    • (with additional options)
      • getDefaultFormState
      • computeDefaults
      • getDefaultBasedOnSchemaType
      • getArrayDefaults

All tests are passed “as is” (except one, see below), but I've left a few notes in the code in obscure places.

I made a change to one test to make it more explicit, see b49e7a3

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 npx nx run-many --target=build --exclude=@rjsf/docs && 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