interpolate template engine into heredoc

Author: joelhawksley

lib/generators/view_component/component/templates/component.rb.tt

@@ -3,9 +3,9 @@
 <% module_namespacing do -%>
 class <%= class_name %><%= options[:skip_suffix] ? "" : "Component" %> < <%= parent_class %>
 <%- if inline_template? -%>
-  <%= template_engine %>_template <<~ERB
+  <%= template_engine %>_template <<~<%= template_engine.upcase %>
     <h1>Hello, World!</h1>
-  ERB
+  <%= template_engine.upcase %>
 <%- end -%>
 <%- if initialize_signature? -%>
   def initialize(<%= initialize_signature %>)

test/sandbox/test/generators/component_generator_test.rb

@@ -142,7 +142,7 @@ def test_invoking_slim_template_engine_inline
     run_generator %w[user --inline --template-engine slim]
 
     assert_file "app/components/user_component.rb" do |component|
-      assert_match(/slim_template/, component)
+      assert_match(/slim_template <<~SLIM/, component)
     end
 
     assert_no_file "app/components/user_component.html.slim"