Enhance CTS for missing VAO bindings

[lexaknyazev]

From WebGL 1.0, Section 6.2:

If a vertex attribute is enabled as an array via enableVertexAttribArray but no buffer is bound to that attribute (generally via bindBuffer and vertexAttribPointer), then draw commands (drawArrays or drawElements) will generate an INVALID_OPERATION error.

The CTS should check that all draw commands enforce this condition: drawArrays, drawElements, drawArraysInstancedANGLE, drawElementsInstancedANGLE, drawArraysInstanced, drawElementsInstanced, drawRangeElements, multiDraw*.