Create builder for ecmascript

[jodinathan]

I couldn't find an official IDL-like file for the builtin JS (ecmascript) stuff like we use here in this package for the W3C bindings.

So today we have a few ecmascript stuff like Reflect that are manually added to the manual.dart file.

Even so, we need to find a way to automate it through a builder.

There are few options right now:

• Use MDN website as source do automation: not reliable. It is good for documentation but not for spec because it is hand made
• Read the AST of TypeScript: Very good for spec, too much work to start and we would still use MDN for documentation. However, this could also open a door to translating TS spec files (.d.ts) to Dart