Upgrade configuration to more modern defaults
- Remove Grunt in favor of running tools like eslint/stylelint from NPM directly. "grunt-banana-checker" provides its own CLI so a Gruntfile is not necessary to use this tool any longer.
- Adds eslint, eslint-plugin-vue, stylelint, eslint-config-wikimedia, and stylelint-config-wikimedia as dev dependencies at their latest versions.
- Updates the .eslintrc file to use the new "client-es6" config as the starting point.
- Removes an unused linter override comment in LookupDemo.vue
Bug: T342043