Offscreen Canvas Support

Hello,

I tried to use Effekseer in a three.js app with an [Offscreen Canvas](https://developer.mozilla.org/en-US/docs/Web/API/OffscreenCanvas) on a web worker today, but failed to make it happen.

First there are multiple usages of `new Image`, e.g. [here](https://github.com/effekseer/EffekseerForWebGL/blob/cec592161de6c631ffaada8704c3d01da7250725/src/js/effekseer.src.js#L497) and [here](https://github.com/effekseer/EffekseerForWebGL/blob/cec592161de6c631ffaada8704c3d01da7250725/src/js/effekseer.src.js#L93) which is not available on web workers. I replaced those with `createImageBitMap()`, but there is still an error thrown *somewhere* in a promise, followed by `[.WebGL-0x11f423912900] GL_INVALID_OPERATION: Must have element array buffer bound.`.

Would it be possible to make Effekseer for WebGL compatible with offscreen canvas rendering? 🙏
Kind Regards