better handling of platforms without a font-manager

What?

Mostly Android and iOS. When you're cross compiling, uname doesn't work, so we needed another system detection mechanism, but overall feature detection is a better idea. This new system will also enable it to work on weird platforms.
Android doesn't have a FontManager like font-config so we needed a dummy.
The findFontOpt API is needed because there is already some cases where findFont can return NULL, and now the dummy also does that, so we needed to handle it, previously it would just crash the entire app. This can also be used to implement a fallback mechanism.