Add AttributeLocation and remove Command.locate()

[yanchith]

Allow caching queried attribute locations with AttributeLocation:

const cmd = ...;
const aPosition = dev.queryAttributeLocation(cmd, "a_position");
const aColor = dev.queryAttributeLocation(cmd, "a_color");

// .index property allows for getting the location
const positionLocation = a_position.index;

// toString() allows for use in computed properties
const attrs = dev.createAttributes(Primitive.TRIANGLES, {
  [aPosition]: [
        [-0.3, -0.5],
        [0.3, -0.5],
        [0, 0.5],
    ],
  [aColor]: [
        [1, 0, 0, 1],
        [0, 1, 0, 1],
        [0, 0, 1, 1],
    ],
});

After implementing we can remove Command.locate() and migrate all examples to use this.