renderbuffer tests

• test renderbufferStorage STENCIL_INDEX811ms ‣

  const {gl} = createContext();
  const tracker = new MemInfoTracker(gl, 'renderbuffer');
  const rb1 = gl.createRenderbuffer();
  tracker.addObjects(1);
  gl.bindRenderbuffer(gl.RENDERBUFFER, rb1);
  let size1a;
  {
    const width = 17;
    const height = 49;
    gl.renderbufferStorage(gl.RENDERBUFFER, gl.STENCIL_INDEX8, width, height);
    size1a = width * height;
    tracker.addMemory(size1a);
  }
  gl.deleteRenderbuffer(rb1);
  tracker.deleteObjectAndMemory(size1a);