Sets up the
WebGLShader.uniforms object, populating it with the names
and locations of the shader uniforms this shader requires.
It works by first calling
gl.getProgramParameter(program, gl.ACTIVE_UNIFORMS) to
find out how many active uniforms this shader has. It then iterates through them,
gl.getActiveUniform to get the WebGL Active Info from each one. Finally,
the name and location are stored in the local array.
This method is called automatically when this class is created.
This WebGLShader instance.