Reasons for making this change

fixes #4297
Using ErrorSchemaBuilder to add errors to arrays results in the wrong format being generated. This PR extends the ErrorSchemaBuilder to support adding, setting and clearing errors that have an array number in their path.
Uses lodash https://lodash.com/docs/4.17.15#setWith to set the numbers as object instead of arrays.

const errorSchemaBuilder = new ErrorSchemaBuilder();
errorSchemaBuilder.addErrors('is required', ['array', 0, 'field']);
errorSchemaBuilder.ErrorSchema

Before change:

{
    "array": [
        {
            "field2": {
                "__errors": [
                    "is required"
                ]
            }
        }
    ]
}

After change:

{
    "array": {
        "0": {
            "field2": {
                "__errors": [
                    "is required"
                ]
            }
        }
    }
}

The following also work

errorSchemaBuilder.addErrors('is required', 'array.0.field');
errorSchemaBuilder.addErrors('is required', ['array', '0', 'field']);
errorSchemaBuilder.addErrors('is required', 'array["0"].field');

This is my first contribution to this repo so open to feedback. Due to timezone differences, I can't attend the meeting.

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 not sure what to add to the change log
• I'm adding a new feature
  • I've updated the playground with an example use of the feature