Add translation and perspective matrices

These matrices are useful to position and project objects in test
programs to verify that uniform passing works properly.

Signed-off-by: Thierry Reding <thierry@gilfi.de>
Implement grate_shader_emit() for dummy backend
gles: Add cube test program

This test program renders a cube transformed via a simple modelview
projection matrix.

Signed-off-by: Thierry Reding <thierry@gilfi.de>
gles: Request 8-bit depth buffers

Require a depth buffer for GLES test programs in order to allow 3D
objects to be rendered properly.

Signed-off-by: Thierry Reding <thierry@gilfi.de>