With ImageInner::StaticTextures (the variant) and StaticTextures (the
struct), we need to disambiguate for the generated enum contructor
functions. This is done by prefixing the enum variant with their name.
Fixes#909
Since we declare the struct in C++, we don't need to declare it in
rust for cbindgen anymore, as long as we expose the Size2D type from
euclid to the cbindgen_private namespace