Function createTimer

createTimer(
should_stop: (cur_time: number, start_time: number) => boolean,
): (
on_frame?: (time: number) => void,
) => { promise: Promise<number>; stop: () => void }
Create rAF timer
Parameters
- should_stop: (cur_time: number, start_time: number) => boolean
Returns (
on_frame?: (time: number) => void,
) => { promise: Promise<number>; stop: () => void }
Example: Basic usage
```
// n_frames
let n_frames = 0;
const timer = createTimer(() => ++n_frames > 3); // show 3 frames

// duration
const frame_ms = 16.67;
const duration = 100; // show 100ms
const timer = createTimer(
  (cur_time, start_time) =>
    cur_time - start_time >= duration - frame_ms / 2,
);
```
- Defined in scene.ts:36