Support cross compile the GL backend code into WASM.
The code needs WebGL 2.0 API so, the compile flags contains `MAX_WEBGL_VERSION` and `FULL_ES3`
Also add binding code to initialize the WebGL context and GLCanvas.
Updated WASM binding to bring WebGPU on the web player.
binding will generate a WASM binary, which can render animation through both SW and WG raster engine.
A raster engine will be chosen by parameter `engine`, when initializing.
enabled options:
- EXPORT_ES6 > to import glue code in es6 module system
- SINGLE_FILE > to build library as a single JS file, single file reduces loading latency
- MODULARIZE > proper option to build es6 module (optimized)
- EXPORTED_RUNTIME_METHODS > allow es6 module based glue code to import FS
