glPixelStorei does not support PACK_ALIGNMENT

This issue originates from https://github.com/emscripten-core/emscripten/issues/21968

Calling glPixelStorei affects the memory layout of pixel data in glTexImage2D, glTexSubImage2D, and glReadPixels, thereby affecting the valid length of the pixel data. The OpenGL documentation provides a more detailed explanation:
https://registry.khronos.org/OpenGL-Refpages/es3.0/html/glPixelStorei.xhtml

Emscripten restricts the length of pixel data through emscriptenWebGLGetTexPixelData, but this restriction may be shorter than expected after calling glPixelStorei. This results in browser errors.
Chrome and Safari:

WebGL: INVALID_OPERATION: texSubImage2D: ArrayBufferView not big enough for request

FireFox:

WebGL warning: texSubImage: Desired upload requires more bytes (20004) than are available (1440). 

The problem with emscriptenWebGLGetTexPixelData is that it does not distinguish between pack and unpack, nor does it handle all possible parameters in glPixelStorei.

My simple patch is：

sed -i'.original' -e 's/return heap.subarray(toTypedArrayIndex(pixels, heap), toTypedArrayIndex(pixels + bytes, heap));/return heap.subarray(toTypedArrayIndex(pixels, heap));/g' emsdk/src/library_webgl.js

This removes the length restriction on the pixel data, since the C API only passes a pointer without data length.

The issue with this patch is that it makes it easier for the pixel data length to exceed 2GB, which in FireFox leads to a new problem:

WebGL2RenderingContext.readPixels: Argument 7 can't be an ArrayBuffer or an ArrayBufferView larger than 2 GB

Inizia da emsdk/src/library_webgl.js, in particolare da emscriptenWebGLGetTexPixelData, e confronta il suo calcolo della lunghezza con il comportamento di pack/unpack in glPixelStorei e con il riferimento OpenGL collegato. Riproduci i casi texSubImage2D e readPixels in Chrome, Safari o Firefox; il lavoro è completo quando la dimensione del buffer è corretta senza errori del browser, incluso il limite di 2 GB di Firefox.