Convert theme switcher to a webcomponent

packages/theme-switcher/.eslintignore

packages/theme-switcher/.eslintrc.json

packages/theme-switcher/.gitignore

packages/theme-switcher/.npmignore

packages/theme-switcher/LICENSE

packages/theme-switcher/README.md

packages/theme-switcher/assets/favicon.ico

packages/theme-switcher/i18next-scanner.config.js

packages/theme-switcher/karma.conf.js

packages/theme-switcher/package.json

packages/theme-switcher/rollup.config.js

packages/theme-switcher/src/dbp-theme-switcher.js

packages/theme-switcher/src/demo.js

packages/theme-switcher/src/i18n.js

packages/theme-switcher/src/i18n/de/translation.json

packages/theme-switcher/src/i18n/en/translation.json

packages/theme-switcher/src/index.js

packages/theme-switcher/src/theme-switcher.js

packages/theme-switcher/test/unit.js

toolkit-showcase/assets/theme-switcher.metadata.json