Export the image pattern and the media pattern algorithm

[sefeng211]

I'd like to reference them in whatwg/fetch#1755, hence this patch to export those two algorithms.

• At least two implementers are interested (and none opposed):
  • This is an editorial thing, I don't think implementers interests are needed
• Tests are written and can be reviewed and commented upon at:
  • Also not needed
• Implementation bugs are filed:
  • Also not needed
• MDN issue is filed: Also not needed
• The top of this comment includes a clear commit message to use.

(See WHATWG Working Mode: Changes for more details.)

---

Preview | Diff