[SolidusAdmin] Fix mock_component helper

The mock component in the ComponentHelpers module was not a real
constant, which messes with ViewComponent's expectations about what
render_inline is given. Using `stub_const` in the helper allows us to
give it an actual name, and view_component > 3.21.0 will work for us.

The helper is only used in the base component spec. I could have spent
more time giving it an optional block, but this solution is the most
straightforward.

(cherry picked from commit 228ca12)

# Conflicts:
#	admin/lib/solidus_admin/testing_support/component_helpers.rb
#	admin/spec/components/solidus_admin/base_component_spec.rb

admin/spec/components/solidus_admin/base_component_spec.rb

@@ -9,7 +9,7 @@
         def call
           icon_tag("user-line")
         end
-      end.new
+      end
 
       render_inline(component)
 
@@ -42,7 +42,7 @@ def call
 
   describe ".stimulus_id" do
     it "returns the stimulus id for the component" do
-      stub_const("SolidusAdmin::Foo::Bar::Component", Class.new(described_class))
+      mock_component("SolidusAdmin::Foo::Bar::Component") { erb_template "" }
 
       expect(SolidusAdmin::Foo::Bar::Component.stimulus_id).to eq("foo--bar")
       expect(SolidusAdmin::Foo::Bar::Component.new.stimulus_id).to eq("foo--bar")

admin/spec/support/solidus_admin/component_helpers.rb

@@ -11,14 +11,9 @@ module ComponentHelpers
     #      "Rendered"
     #    end
     #  end
-    def mock_component(&definition)
-      Class.new(SolidusAdmin::BaseComponent) do
-        # ViewComponent will complain if we don't fake a class name:
-        # @see https://github.com/ViewComponent/view_component/blob/5decd07842c48cbad82527daefa3fe9c65a4226a/lib/view_component/base.rb#L371
-        def self.name
-          "Foo"
-        end
-      end.tap { |klass| klass.class_eval(&definition) if definition }
+    def mock_component(class_name = "Foo::Component", &definition)
+      component_class = stub_const(class_name, Class.new(described_class, &definition))
+      component_class.new
     end
   end
 end