Move all remaining members of nsIPresShell to mozilla::PresShell

Additionally, this sorts out the order of member variables for minimizing the
instance size.

And also this changes `enum RenderFlags` to `enum class RenderingStateFlags`.

Differential Revision: https://phabricator.services.mozilla.com/D29312

components/style/gecko/media_queries.rs

@@ -169,7 +169,6 @@ impl Device {
             self.document()
                 .mPresShell
                 .as_ref()?
-                ._base
                 .mPresContext
                 .mRawPtr
                 .as_ref()