Rename lang-files to lang-dir, remove unnecessary attributes

packages/app-shell/src/app-shell.js

packages/common/dbp-common-demo.js

packages/common/src/i18n.js

packages/common/src/translation.js

toolkit-showcase/assets/common.metadata.json

toolkit-showcase/assets/dbp-toolkit-showcase.html.ejs

toolkit-showcase/assets/i18n/de/translation.json

toolkit-showcase/assets/i18n/en/translation.json

toolkit-showcase/assets/i18n/overrides/de/translation.json

toolkit-showcase/assets/i18n/overrides/en/translation.json

...showcase/assets/translation-overrides/de/translation.json

...showcase/assets/translation-overrides/en/translation.json

toolkit-showcase/rollup.config.js

toolkit-showcase/src/dbp-common-demo-activity.js