Debug symbols don't work in platform=web

### Godot version

4.4.dev4.official.36e6207bb

### godot-cpp version

5255034fb0c8914da22b80209a3085be33742776

### System information

tried in both Chrome Stable and Firefox-ESR; wasm was compiled on debian trixie and ubuntu noble

### Issue description

Debug symbols do not appear to work for gdextensions in wasm+template_debug builds.

Even after adding `-gdwarf-4 -g3` as the base godot SConstruct script does () and ensuring a full rebuild and that the parameters made it to emcc and the linker, the browser still did not show symbols on the stack trace for a crash.

### Steps to reproduce

1. Export the gdextension and project in debug mode for web
2. Open the web browser's debugging tools
3. Pause execution during a call to the gdextension (or add a statement in the gdextension that crashes and tell the browser to pause on exceptions)
4. Only the base engine wasm file will have symbols loaded

### Minimal reproduction project

(if needed, I can provide one, but it works the same for any project)