Want to start documenting things we need to do when Babel 7 is ready.

• Enable runtime transform for helpers with { polyfill: false, useBuiltIns: true, useESModules: true }, see Add useBuiltIns and useESModules options to transform-runtime babel/babel#5442 for context and babel-runtime helpers should not pull in unnecessary polyfills (T7519) babel/babel#4418 for why we couldn't do it before
• We should probably enable transform-inline-elements in production and bundle Symbol polyfill (?).
• Helpers: true (see below)