Additionally, this patch makes `nsFrame.h` stop including `nsIPresShell.h`
and makes each users include `mozilla/PresShell.h` instead.  So, this improves
rebuild performance of `nsIPresShell.h` (and `mozilla/PresShell.h` in the
future).

Note that due to `nsIFrame::PresShell()`, `mozilla::` prefix is necessary for
`PresShell` in a lot of classes which are derived from `nsIFrame` even in
`.cpp` files.

Differential Revision: https://phabricator.services.mozilla.com/D27476

--HG--
extra : moz-landing-system : lando