FIX: Allow theme translations to be accessed in initializers (#8285)

Previously theme translations were loaded along with other plugin API scripts. These run after pre-initializers and initializers when the app boots. This commit moves theme translation loading into pre-initializers, so their behaviour matches core translations more closely.

lib/theme_javascript_compiler.rb

@@ -208,8 +208,8 @@ class ThemeJavascriptCompiler
     @content << script + "\n"
   end
 
-  def append_module(script, name)
-    script.prepend theme_variables
+  def append_module(script, name, include_variables: true)
+    script = "#{theme_variables}#{script}" if include_variables
     template = Tilt::ES6ModuleTranspilerTemplate.new {}
     @content << template.module_transpile(script, "", name)
   rescue MiniRacer::RuntimeError => ex