Test TypeScript blueprints using TypeScript enabled Ember apps #20362
Description
Even though we had enabled the EMBER_TYPESCRIPT_BLUEPRINTS flag when running blueprint tests, and have now enabled that flag by default, we still don't actually verify the generation of TypeScript files. That is because all the Ember apps during tests are generated without the --typescript flag. To test the TypeScript blueprints correctly, we must use TypeScript enabled Ember apps.
NOTE: We don't necessarily have to create these apps using the --typescript flag, as we would run into ember-cli/ember-cli#10045 I think (would make running those tests a lot slower). Making sure that the isTypeScriptProject option in the .ember-cli file is set to true should be sufficient as well I think.