closes https://linear.app/tryghost/issue/PLG-176
The editor files were previously stubbed for testing because we didn't have a way to load the externally-hosted files. This made testing slow and difficult because the only way to test the Admin integration was via Ghost's e2e browser tests.
- unstubbed the editor globals so `fetchKoenigLexical()` actually tries to import the external assets
- updated `ember-cli-build` to copy the Koenig UMD file over to the assets directory in development/test builds
- updated `environment.js` to set the required filename for the default asset import to successfully hit the test environment hosted files
- updated lexical editor acceptance tests to demonstrate the editor loads successfully for new and existing posts
fc501add94