* The styles queue has always been top-only
(except for a few months in 2015).
* The top queue loads asynchronous since mid-2015. (T107399)
And LocalStorage eval, previously the last remaining non-async part
of module loading, is also async as of October 2016. (T142129)
* This change merges the bottom 'mw.loader.load()' queue with the top queue.
It also moves any other snippets potentially in the bottom queue still:
- embed: I couldn't find any private modules with position=bottom
(doesn't make sense due to their blocking nature). If any do exist,
(third-party extensions?), they'll now be embedded in the <head>.
- scripts: Any legacy 'only=scripts' requests will now initiate
from the <head>.
Bug: T109837
Change-Id: I6c21e3e47c23df33a04c42ce94bd4c1964599c7f
bc374082fa