Note that we need to allow clients to find out if compressed textures
are supported BEFORE the engine is created, so that they can start
downloading the correct set of texture files. To allow this, we now
expose a getSupportedFormats function that creates a throw-away canvas
in order to query extensions (creating a temporary canvas is a technique
that we also used in the old PNG decoder that we removed in 7b36ed4)
These are broken and no longer necessary now that we have web/samples.
Despite the name, these weren't real tests; they were ignored by CMake
and did not run in an automated manner. Going forward we need a better
solution for automated testing.
