renderbuffer tests

• test renderbufferStorageMultisample15ms ‣

  const {gl} = createContext2();
  if (!gl) {
    return;
  }
  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.renderbufferStorageMultisample(gl.RENDERBUFFER, 2, gl.RGB565, width, height);
    size1a = width * height * 2 * 2;
    tracker.addMemory(size1a);
  }
  let size1b;
  {
    const width = 37;
    const height = 9;
    gl.renderbufferStorageMultisample(gl.RENDERBUFFER, 4, gl.DEPTH_COMPONENT16, width, height);
    size1b = width * height * 2 * 4;
    tracker.addMemory(size1b - size1a);
  }
  const rb2 = gl.createRenderbuffer();
  tracker.addObjects(1);
  gl.bindRenderbuffer(gl.RENDERBUFFER, rb2);
  let size2;
  {
    const width = 71;
    const height = 94;
    gl.renderbufferStorageMultisample(gl.RENDERBUFFER, 2, gl.RGBA4, width, height);
    size2 = width * height * 2 * 2;
    tracker.addMemory(size2);
  }
  gl.deleteRenderbuffer(rb1);
  tracker.deleteObjectAndMemory(size1b);
  gl.deleteRenderbuffer(rb2);
  tracker.deleteObjectAndMemory(size2);