Test that we can transform code using modern language features

[domenic]

In particular, private fields and imports are both worth testing. A simple test of the console-stripper that uses both those features would suffice to close this issue.

This might require changing the parser that jscodeshift uses, e.g. using https://github.com/facebook/jscodeshift/#parser.

[domenic]

At this point we are blocked on microsoft/TypeScript#30829, which is pretty active and should land soon. Then we'll need to wait on a new TypeScript release; those seem to happen about once a month or so.