math/mathwfd.h forward declares all {mat|vec}{2|3|4}<> classes,
which allows us to remove their respective #include in a lot of
our public headers.
Our math headers are full of templates, so this should help build times
a bit.
Also we want to keep the public headers as minimalist as possible.
Note that libgeometry is already included in `filament-android`, this
simply exposes more of its existing functionality.
The Java version of SurfaceOrientation is similar to the JavaScript
version because we are bundling it into the main Filament package, even
though it is a separate library in C++. This is much simpler than
creating a brand new Java package.
New Android sample that tests this is forthcoming.
Fixes#1729.
