[shell] [web] Temporary workaround for shell.html <canvas> CSS width

[asdqwe]

Ref: #4464

Temporary workaround for canvas.emscripten { width: 100%; } CSS not working with current emscripten (3.1.70).
Revert this change when the issue is fixed upstream.

1. Found out that the <canvas> width can be resized with CSS, but only after it's loaded.
2. The issue could be related to $GLFW_Window: function that now takes the framebuffer's width/height as separated parameters (ref1, ref2).
3. Hooked this workaround to Module.setStatus because it was the only Module option I found that runs (consistently) after the canvas finishes loading.

[asdqwe]

Unfortunately (upon more testing) this workaround only handles the canvas size. The mouse input is still wrong (unscaled). Closing the PR because the workaround is insufficient.