Chore: Convert ArrayField to functional components

[heath-freenome]

Reasons for making this change

The work to convert ArrayField to stateless funcitonal components with some breaking changes

• In @rjsf/utils:
  • BREAKING CHANGE: Updated ArrayFieldItemButtonsTemplateType to replace the onAddIndexClick(), onCopyIndexClick(), onDropIndexClick() and onReorderClick() callback-generator props with the onAddItem(), onCopyItem(), onMoveUpItem(), onMoveDownItem() and onRemoveItem() callback props
  • BREAKING CHANGE: Updated ArrayFieldItemTemplateType to change key: string to itemKey: string to avoid a name collision with React
  • BREAKING CHANGE: Updated ArrayFieldTemplateProps to change the type of the items prop from ArrayFieldItemTemplateType<T, S, F>[] to ReactElement[]
• In @rjsf/core:
  • Updated ArrayField to refactor code from a class component to seven stateless functional components, replacing the 4 generator-props with the 5 memoized props mentioned in the @rjsf/utils changes
    • BREAKING CHANGE: The refactor included rendering the ArrayFieldItemTemplate directly by the ArrayField rather than deferring it to the ArrayFieldTemplate
    • Updated the ArrayField tests to adjust for the rendering change AND to remove 2 tests due to them no longer being valid
  • BREAKING CHANGE: Updated ArrayFieldTemplate to remove the ArrayFieldItemTemplate render in favor of simply using items due to ArrayField changes
  • BREAKING CHANGE: Updated ArrayFieldItemButtonsTemplate to replace the old callback-generator functions with the new memoizable callback functions
  • Fixed a bug in Form to avoid getting errors being reported at the root level via onChange when there aren't
• In the rest of the themes, updated ArrayFieldTemplate to remove the ArrayFieldItemTemplate render in favor of simply using items due to ArrayField changes (BREAKING CHANGES)
• Updated the customArray sample to refactor out a ArrayFieldItemButtonsTemplate
• Updated the custom-templates.md documentation to reflect the ArrayField conversion changes
• Updated the v6.x upgrade guide.md documentation to add the BREAKING CHANGES to ArrayFieldTemplateProps, ArrayFieldItemTemplateType and ArrayFieldItemButtonsTemplateType
• Updated the CHANGELOG.md accordingly

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

[heath-freenome]

Since we've made such a large set of breaking changes, I figured we don't need to maintain this anymore

[nickgros]

Suggested change

	- `ArrayFieldItemTemplateProps`: The properties of each element in the ArrayFieldTemplateProps.items array. NOTE: `ArrayFieldTemplateItemType` is an alias to this type
	- `ArrayFieldItemTemplateProps`: The properties of each element in the ArrayFieldTemplateProps.items array.