[New feature] add config to remove (or mark optional) some interfaces for a target browser version

[jzhan-canva]

I did a POC in a local fork, it can configure a browser target, say Chrome 75, then it will mark APIs optional if they don't exist in chrome 75
If you think this is useful, I can create a PR for such feature

[jakebailey]

We bundle only one version with TypeScript, and are unlikely to publish copies for anything but latest. This tool isn't really intended to be used by hand otherwise, so I'm not sure we'd need this?

[jakebailey]

(in the age of evergreen browsers, I don't really know who needs to target older ones who aren't in some condition where they really need other testing too...)