Add "importRuntime" option to "transform-runtime"

[nicolo-ribaudo]

When "importRuntime" is true, regenerator doesn't assume that
regeneratorRuntime is available globally, but it injects an import
statement (or require, depending on the source type)

Example output:

var _regeneratorRuntime = require("regenerator-runtime");

var _marked =
/*#__PURE__*/
_regeneratorRuntime.mark(f);

function f() {
  return _regeneratorRuntime.wrap(function f$(_context) {
    while (1) switch (_context.prev = _context.next) {
      case 0:
      case "end":
       return _context.stop();
    }
  }, _marked, this);
}

I had to update the Babel deps because I hit babel/babel#8508 and babel/babel#8722.

[nicolo-ribaudo]

This changes were made by lerna I think.

[benjamn]

Should we revert the lerna changes?

[benjamn]

This seems like the right direction, though I have one substantive suggestion.

[benjamn]

Now that runtimeProperty takes options and does more than just construct a member expression, I think we should move it out of util.js and make it a method of the Emitter class. That way we won't need to pass the options explicitly, since they're stored as a property of the Emitter object now. From what I can tell, everywhere runtimeProperty was previously called, we have access to an Emitter instance, so this change should be pretty straightforward. What do you think @nicolo-ribaudo?

[loganfsmyth]

To throw it out there, I don't have a problem with landing this if you want, but I don't think it's something we'd recommend people use on the Babel side since plugin-transform-runtime also handles injecting a reference to the runtime and is already very recommended in Babel 7.