rewrite script with TS

[g-plane]

• rewrite with TypeScript
• use more async operations
• use Promise.all to enable concurrency

[antfu]

Thanks a lot for working on this! One thing to mention is that those files are generteted from the template. You may want to update them too to help more people benefit from it. Thanks!

https://github.com/microsoft/TypeScript-Website/tree/v2/packages/create-typescript-playground-plugin
https://github.com/microsoft/TypeScript-Playground-Samples