Flatten the character count and form group divs

The update guidance says that the outer character count div should now
be merged with the form group, like this:

  HTML before:

  <div class="govuk-character-count" data-module="govuk-character-count" data-maxlength="100">
    <div class="govuk-form-group">
      <!-- // Label, hint, error and textarea -->
    </div>
    <!-- // Count message -->
  </div>

  HTML after:

  <div class="govuk-form-group govuk-character-count" data-module="govuk-character-count" data-maxlength="100">
    <!-- // Label, hint, error, textarea and count message -->
  </div>

This allows us to simplify the code considerably and get rid of the
character count container completely.

lib/govuk_design_system_formbuilder/elements/text_area.rb

@@ -13,6 +13,8 @@ class TextArea < Base
       def initialize(builder, object_name, attribute_name, hint:, label:, caption:, rows:, max_words:, max_chars:, threshold:, form_group:, **kwargs, &block)
         super(builder, object_name, attribute_name, &block)
 
+        fail ArgumentError, 'limit can be words or chars' if max_words && max_chars
+
         @label           = label
         @caption         = caption
         @hint            = hint
@@ -25,19 +27,13 @@ def initialize(builder, object_name, attribute_name, hint:, label:, caption:, ro
       end
 
       def html
-        Containers::CharacterCount.new(@builder, **character_count_options).html do
-          Containers::FormGroup.new(*bound, **@form_group).html do
-            safe_join([label_element, supplemental_content, hint_element, error_element, text_area, limit_description])
-          end
+        Containers::FormGroup.new(*bound, **@form_group.merge(limit_form_group_options)).html do
+          safe_join([label_element, supplemental_content, hint_element, error_element, text_area, limit_description])
         end
       end
 
     private
 
-      def character_count_options
-        { max_words: @max_words, max_chars: @max_chars, threshold: @threshold }
-      end
-
       def text_area
         @builder.text_area(@attribute_name, **attributes(@html_attributes))
       end
@@ -92,6 +88,27 @@ def limit_description_id
 
         limit_id
       end
+
+      def limit_form_group_options
+        return {} unless limit?
+
+        {
+          class: %(#{brand}-character-count),
+          data: { module: %(#{brand}-character-count) }.merge(**limit_max_options, **limit_threshold_options).compact
+        }
+      end
+
+      def limit_max_options
+        if @max_words
+          { maxwords: @max_words }
+        elsif @max_chars
+          { maxlength: @max_chars }
+        end
+      end
+
+      def limit_threshold_options
+        { threshold: @threshold }
+      end
     end
   end
 end

spec/govuk_design_system_formbuilder/builder/text_area_spec.rb

@@ -93,7 +93,7 @@
       let(:max_words) { 20 }
       subject { builder.send(*args, max_words:) }
 
-      specify 'should wrap the form group inside a character count tag' do
+      specify 'adds the character count class and data attributes to the form group' do
         expect(subject).to have_tag(
           'div',
           with: {