[5.x] Allow form fields view to be rendered with single tag

[jasonvarga]

Currently in a form:create tag pair, you can loop over the fields to output predefined html for each field. However, you still have to add the label, instructions, errors, etc.

This PR allows you to use the fields var as a single tag and it will output an entire view for you.

-{{ fields }}
-  <div>
-    <label>{{ display }}</label>
-    {{ field }}
-  </div>
-{{ /fields }}
+{{ fields /}}

The view has basic tailwind based markup, just like the individual fields already do. You may override this view in the same way too by adding resources/views/vendor/statamic/forms/fields.antlers.html.

The view was already in the codebase but never used. Maybe the intention was to do exactly this but it never happened. This PR also tweaks the view a little sto improve padding and to honor configured instruction placement.