Downstream the streams fork work

[guybedford]

We run a fork of the SpiderMonkey streams implementation on the SpiderMonkey tree.

We've discussed various approaches to resolving this in the past, but perhaps the most expedient at this point for moving off of maintaining a patchset and being able to more easily update SpiderMonkey would be to inline the streams implementation entirely in the StarlingMonkey tree.

The most difficult thing about this will be shifting the implementation to use external SpiderMonkey patterns as opposed to internal ones, as we are currently using internal headers files.

It would be important when evaluating this project to determine how difficult that would be.