Add CameraFeed support for Web

[shiena]

fixed: godotengine/godot-proposals#12493

Current Limitation:
The platform/web/js/libs/library_godot_camera.js library includes certain functionalities that are inherently asynchronous. We are currently investigating how to execute these functions synchronously, as this is a requirement for our project, but haven't yet found a solution.
I was able to build with JSPI and call asynchronous functions synchronously in Chrome. However, JSPI only works in Chrome and Edge 137.
https://webassembly.org/features/
https://learn.microsoft.com/en-us/microsoft-edge/web-platform/release-notes/137#javascript-promise-integration-jspi-in-webassembly

[shiena]

I've tried enabling Asyncify as follows, which I believe should fix it, but the build is still failing.

diff --git a/platform/web/SCsub b/platform/web/SCsub
index cf872e65ff..5bb105e1cd 100644
--- a/platform/web/SCsub
+++ b/platform/web/SCsub
@@ -106,6 +106,8 @@ else:
     sys_env.Append(LIBS=["idbfs.js"])
     build = sys_env.add_program(build_targets, web_files + ["web_runtime.cpp"])
 
+sys_env.Append(LINKFLAGS=["-sASYNCIFY=1"])
+
 sys_env.Depends(build[0], sys_env["JS_LIBS"])
 sys_env.Depends(build[0], sys_env["JS_PRE"])
 sys_env.Depends(build[0], sys_env["JS_POST"])

cache:INFO: generating system asset: symbol_lists/8eab473934c10451394fc82e8912c6b3712c9ff9.json... (this will be cached in "C:\Users\shien\dev\emsdk\upstream\emscripten\cache\symbol_lists\8eab473934c10451394fc82e8912c6b3712c9ff9.json" for subsequent builds)
cache:INFO:  - ok
unexpected expression type
UNREACHABLE executed at C:\b\s\w\ir\cache\builder\emscripten-releases\binaryen\src\passes\Asyncify.cpp:1142!
em++: error: 'C:/Users/shien/dev/emsdk/upstream\bin\wasm-opt --strip-target-features --post-emscripten -Os --low-memory-unused --asyncify --pass-arg=asyncify-propagate-addlist --pass-arg=asyncify-imports@env.invoke_*,env.__asyncjs__*,*.fd_sync,*.emscripten_promise_await,*.emscripten_idb_load,*.emscripten_idb_store,*.emscripten_idb_delete,*.emscripten_idb_exists,*.emscripten_idb_clear,*.emscripten_idb_load_blob,*.emscripten_idb_store_blob,*.emscripten_sleep,*.emscripten_wget_data,*.emscripten_scan_registers,*.emscripten_lazy_load_code,*._load_secondary_module,*.emscripten_fiber_swap,*.SDL_Delay --zero-filled-memory --pass-arg=directize-initial-contents-immutable --no-stack-ir bin\godot.web.template_debug.wasm32.nothreads.wasm -o bin\godot.web.template_debug.wasm32.nothreads.wasm -g --mvp-features --enable-bulk-memory --enable-exception-handling --enable-multivalue --enable-mutable-globals --enable-reference-types --enable-sign-ext --enable-simd' failed (returned 3221226505)
scons: *** [bin\godot.web.template_debug.wasm32.nothreads.js] Error 1

[Calinou]

Asyncify makes binaries a lot larger, so we need to be able to use it selectively only for functions that need it.

cc @adamscott

[shiena]

Ready for review.
The demo site requires Chrome 137+ due to its use of JSPI.
I wanted to use ASYNCIFY=1 in SCsub but ran into errors, so I'm currently using ASYNCIFY=2 for JSPI.

Demo site: https://shiena.github.io/GodotCameraFeedSample/
Demo source code: https://github.com/shiena/GodotCameraFeedSample

[Faless]

The demo site requires Chrome 137+ due to its use of JSPI.
I wanted to use ASYNCIFY=1 in SCsub but ran into errors, so I'm currently using ASYNCIFY=2 for JSPI.

This means it can't be merged, we at least want support the latest version of Chrome, Firefox and iOS (and we also try to support the latest version of Firefox ESR, but that has been on and off in the past).

That said, it should be possible to implement the API by relying on callbacks instead of requiring asyncify.

[Faless]

We shouldn't use the EM_*_JS functions, as they break dynamic linking.

[shiena]

That said, it should be possible to implement the API by relying on callbacks instead of requiring asyncify.

I'm trying to get a list of CameraFeed objects using CameraServer.feeds() after setting CameraServer.monitoring_feeds = true in GDScript. Once I have a CameraFeed, I then want to retrieve its available formats using CameraFeed.formats.

However, both of these methods return a JavaScript Promise, which makes using callbacks inherently slow.
If there's an alternative approach, I'd be happy to try it out immediately.