Render to offscreen canvas for VGG runtime wasm version

[harry75369]

Detailed description

Currently VGG runtime wasm version is only able to render to a normal canvas node. This will slow down the main process and will even stop the webpage responding.

Rendering to an offscreen canvas may help solve this problem.

Possible implementation

More research should be carried out how to achieve this goal. As far as I know, emscripten + SDL currently do not support offscreen canvas.

Additional information

No response