Fix 4676 - Add support for arrays in the LayoutGridField

[heath-freenome]

Reasons for making this change

Fixes #4676 by adding support for indexes into the LayoutGridField

• Updated LayoutGridField to add support for arrays
• Updated the LayoutGridField to add 100% validation for the new arrays code

Using the schema in the LayoutGridField tests and this uiSchema...

{
  "ui:field": "LayoutGridField",
  "ui:layoutGrid": {
    "ui:row": {
      "spacing": 2,
      "children": [
        {
          "ui:col": {
            "size": 12,
            "children": [
              "example"
            ]
          }
        },
        {
          "ui:columns": {
            "size": 4,
            "children": [
              {
                "name": "example.0.0",
                "fullWidth": true
              },
              {
                "name": "example.0.1",
                "fullWidth": true
              },
              {
                "name": "example.0.2",
                "fullWidth": true
              }
            ]
          }
        }
      ]
    }
  },
  "example": {
    "ui:field": "LayoutHeaderField"
  }
}

One gets the following UI:

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

[nickgros]

this test title is also not accurate

[heath-freenome]

oops, copy pasta