Any parameters (key/value pairs after the '?' in a URL) that have a keyname
that starts with `SDL_` will be put into Emscripten's environment variable
emulation table at startup, before SDL_main runs.
This lets users set hints the same way they might set them from a shell's
command line on a desktop platform:
For example:
`https://example.com/my_sdl3_application.html?SDL_RENDER_DRIVER=software`
Fixes#10154.
f338fa20dd