Use global locale for starter projects

There's currently a caching issue when switching between locales on the project site [1]. To fix this we can only load the project if it has the expected locale.

However, this would break caching for projects that aren't localized. The code editor only uses the project cache when you've not yet logged in or saved a project. The projects you're likely to be editing in this case are the blank starter projects. Since these projects are blank with no instructions they aren't really localizable so I have decided to flag them as having a 'global' localization.

Adding this to the list of locales will mean we can also set this on any imported projects we want this behaviour for.

I'll amend [1] to allow using the cache when when the project is set to global.

### After deploy

Deploy separate migration to update locale for the two blank projects.

[1] RaspberryPiFoundation/editor-ui#1342

Author: zetter-rpf

lib/locales.rb

@@ -18,7 +18,7 @@ def load_locales
         pt-PT ro-RO ru-RU sh-ZW si-LK sk-SK sl-SI so-SO sq-AL sr-SP sv-SE sw-KE ta-IN te-IN th-TH tr-TR tt-RU uk-UA ur-PK vi-VN vls-BE xh-ZA zh-CN zh-TW
       ]
       I18n.default_locale = :en
-      I18n.available_locales = two_letter_locales + four_letter_locales
+      I18n.available_locales = two_letter_locales + four_letter_locales + [:global]
     end
   end
 end

lib/project_loader.rb

@@ -5,7 +5,7 @@ class ProjectLoader
 
   def initialize(identifier, locales)
     @identifier = identifier
-    @locales = [*locales, 'en', nil]
+    @locales = [*locales, 'global', 'en', nil]
   end
 
   def load(include_images: false)

lib/tasks/project_components/blank_html_starter/project_config.yml

@@ -1,6 +1,7 @@
 NAME: 'Blank HTML & CSS Starter'
 IDENTIFIER: 'blank-html-starter'
 TYPE: 'html'
+LOCALE: 'global'
 COMPONENTS:
   - name: 'index'
     extension: 'html'

lib/tasks/project_components/blank_python_starter/project_config.yml

@@ -1,6 +1,7 @@
 NAME: 'Blank Python Starter'
 IDENTIFIER: 'blank-python-starter'
 TYPE: 'python'
+LOCALE: 'global'
 COMPONENTS:
   - name: 'main'
     extension: 'py'

spec/lib/project_loader_spec.rb

@@ -41,6 +41,14 @@
     end
   end
 
+  context 'when global project with identifier exists' do
+    let!(:global_project) { create(:project, identifier:, locale: 'global') }
+
+    it 'defaults to global' do
+      expect(loaded_project).to eq(global_project)
+    end
+  end
+
   context 'when no preferred locale or English versions but user version exists' do
     let!(:user_project) { create(:project, identifier:, locale: nil) }