Can't build for WebGL2

[yueyuzhao]

Hi, thanks for this awesome library!
But I can't build WebGL2 and it seems to me that there are some files that are missing in this library.
Here are the logs:

[572/572] link path_fiddle.js
FAILED: path_fiddle.js 
em++ -o path_fiddle.js obj/default/path_fiddle/fiddle_context_d3d.o obj/default/path_fiddle/fiddle_context_dawn.o obj/default/path_fiddle/fiddle_context_gl.o obj/default/path_fiddle/fiddle_context_vulkan.o obj/default/path_fiddle/path_fiddle.o librive.a librive_pls_renderer.a librive_decoders.a liblibpng.a libzlib.a liblibjpeg.a librive_harfbuzz.a librive_sheenbidi.a librive_yoga.a -flto -sALLOW_MEMORY_GROWTH=1 -sDYNAMIC_EXECUTION=0 -sWASM=1 -sUSE_GLFW=3 -sMIN_WEBGL_VERSION=2 -sMAX_WEBGL_VERSION=2 --preload-file /home/gold/rivs@/
error: /home/gold/rivs@/ does not exist
em++: error: '/home/circleci/project/submodules/rive-cpp/build/dependencies/emsdk/upstream/emscripten/tools/file_packager path_fiddle.data --from-emcc --preload /home/gold/rivs@/' failed (returned 1)
ninja: build stopped: subcommand failed.

Exited with code exit status 1

Code that I think related to the error:
https://github.com/rive-app/rive-renderer/blob/a7407663c3e4425703373d92bdf34037b9906d7d/premake5.lua#L136-L146
You can view the full logs from here: https://app.circleci.com/pipelines/github/double-pi/rive-renderer/8/workflows/1a8d2399-3cf9-4e67-9924-47da5bb028d2/jobs/9

[joelphilippage]

I had a similar issue and had to clone the cpp package to the folder inside submodules for the renderer as well as the WASM submodules folder.