Fixes #4335

Describe your changes

Fairly extensive changes to how array properties are handled in JSON Form Widget. Arrays, whether "simple" (an array of strings or numbers) or "complex" (arrays of objects) will contain one more level of nested fieldsets. This is because each array item now has its own action buttons, so that array items can be removed or moved in the order. Previously we only had action buttons at the end of the array, allowing us to "add one" or "remove one".

Because the autoselect widgets expect a built array fieldset and then rewrite it, there are also a number of changes to that logic. A risk - we do not really have full functional test coverage for these elements. Also, now that I understand the code flow a bit better, it does make me wonder if there's a better approach that avoids building all these nested fieldsets on the first pass only to flatten and replace them on the second pass with WidgetRouter.

QA Steps

• Create a new Dataset
• Add several distributions
• Re-order them, remove distributions from the beginning or middle of the list
• Do the same for "References"
• Confirm that the keyword and topic fields continue to work as expected
• Save the dataset, and view the JSON in the API to confirm all works as expected
• Edit an existing dataset, and try similar tests

You may want to remove some fields from the distribution schema to make that form element shorter - Keep it to just title, description and downloadURL for instance.

Note on codeclimate failure - ArrayHelper is pretty big now but I don't see an obvious way to split it up that would make the code much more readable. Open to suggestions but IMO let's just let it slide for now and revisit if the method count gets any higher.

Checklist before requesting review

If any of these are left unchecked, please provide an explanation

• I have updated or added tests to cover my code
• I have updated or added documentation