Upgrade tsconfig target to es6?

[peterm-canva]

Can we upgrade the tsconfig target to es6, and remove "useDefineForClassFields": true?

It helps parse time, runtime performance and transpiled size to use es6 features natively rather than the transpiled versions.

This saves 300 lines of code in the transpiled output.

I'm not sure if there's any minimum target environment for this project, but es6 has been around a long time now, and there's a benefit to bumping the target.

Happy to send a PR if this is workable.