[OP-19415] Primer patterns in FilterFormComponent

Uses `ConditionalWrapper` to eliminate template duplication in the
`wrap_with_controller` branch, and `merge_data` from
`Primer::AttributesHelper` for Stimulus data attributes.

https://community.openproject.org/wp/OP-19415

lookbook/docs/patterns/11-filter-forms.md.erb

@@ -98,9 +98,10 @@ The host server receives the canonical string in
 
 ### Combining with non-filter inputs
 
-`FilterFormComponent` composes with other forms via
-`Primer::Forms::FormList`. All children share the same builder and
-therefore submit through the same `<form>`.
+`FilterFormComponent` is rendered next to normal Primer form objects, not
+inside `Primer::Forms::FormList`. Render any regular form objects through
+a `FormList`, then render `FilterFormComponent` with the same builder. All
+fields still submit through the same surrounding `<form>`.
 
 <%= embed OpenProject::Filter::FilterFormPreview, :combined_with_other_inputs, panels: %i[preview source] %>
 

lookbook/previews/open_project/filter/filter_form_preview/combined_with_other_inputs.html.erb

@@ -1,6 +1,7 @@
-<%# `Filters::FilterFormComponent` is a component — combine it with %>
-<%# other forms in a single `Primer::Forms::FormList` to share one builder %>
-<%# (and therefore one submission) with non-filter inputs. %>
+<%# `Filters::FilterFormComponent` is a ViewComponent that shares the %>
+<%# surrounding Primer form builder with other form objects. Render normal %>
+<%# Primer form objects through FormList, then render the filter component %>
+<%# next to that list with the same builder. %>
 <%
   note_form = Class.new(ApplicationForm) do
     form do |f|
@@ -9,17 +10,13 @@
   end
 %>
 <%= primer_form_with(url: "/foo", method: :post) do |f| %>
-  <%=
-    render(
-      Primer::Forms::FormList.new(
-        note_form.new(f),
+  <%= render(Primer::Forms::FormList.new(note_form.new(f))) %>
+  <%= render(
         Filters::FilterFormComponent.new(
           builder: f,
           query: query,
           wrap_with_controller: true,
           hidden_input_name: "filters"
         )
-      )
-    )
-  %>
+      ) %>
 <% end %>