Promise chaining the emscripten module `then` function breaks it badly,
causing an infinite loop.
I'm unsure about the source of the issue, but most likely at this point
is due to the old emscripten version (I remember very old html5 builds
having issue with promise chaining too).
With this commit, we no longer use the module as a promise, and
instantiate it using `Promise` objects directly for compatibility.
`WebAssembly.instantiateStreaming` requires the mime-type to be
`application/wasm`, but some servers (including most debug servers) do
not provide the content-type header.
This commit forces it via JavaScript, by creating a `Response` object
with the `wasm` content, and explicitly defined `content-type` header.
This allow the loading bar to be much more reliable, even in cases where
realible stream loading status is not detectable (server-side
compression, chunked encoding).
Initial work to make liniting easier.
This includes:
- Rename http_request.js to library_godot_http_request.js.
- Rename externs.js to engine.externs.js.
- New library_godot_runtime.js (GodotRuntime) wraps around emscripten
functions.
- Refactor of XMLHttpRequest handler in engine/preloader.js.
- Few fixes to bugs spotted by early stage linting.
