Document tag.attributes helper

The `tag.attributes` helper introduced in [rails#40657][] is implemented on a
`:nodoc:`-private `TagBuilder` class, so the documentation for the
method is omitted when generating the API Guides HTML pages.

This commit extends the `ActionView::Helpers::TagHelper` module
documentation comment to mention the new attribute building
capabilities, along with some examples.

[rails#40657]: rails#40657

Author: seanpdoyle

actionview/lib/action_view/helpers/tag_helper.rb

@@ -235,6 +235,20 @@ def method_missing(called, *args, **options, &block)
       #   # A void element:
       #   tag.br  # => <br>
       #
+      # === Building HTML attributes
+      #
+      # Transforms a Hash into HTML attributes, ready to be interpolated into
+      # ERB. Includes or omits boolean attributes based on their truthiness.
+      # Transforms keys nested within
+      # <tt>aria:</tt> or <tt>data:</tt> objects into `aria-` and `data-`
+      # prefixed attributes:
+      #
+      #   <input <%= tag.attributes(type: :text, aria: { label: "Search" }) %>>
+      #   # => <input type="text" aria-label="Search">
+      #
+      #   <button <%= tag.attributes id: "call-to-action", disabled: false, aria: { expanded: false } %> class="primary">Get Started!</button>
+      #   => <button id="call-to-action" aria-expanded="false" class="primary">Get Started!</button>
+      #
       # === Legacy syntax
       #
       # The following format is for legacy syntax support. It will be deprecated in future versions of Rails.