Some assets are loaded based on OS/server feature detection, namely
textures (but potentially others).
The ResourceImporter will fail to load a texture if the OS reports not
supporting it. The OS, in turn, checks texture format support via the
RenderingServer.
This commit makes the dummy rasterizer report known texture formats as
supported (although unused), so that scenes can be correctly loaded when
they include references to imported textures.
Fabio Alessandrelli
e880294d9f