fix: Rename Dispatcher global name to avoid conflicts with Nitro

[mrousavy]

Since WebGPU uses an early copy of Nitro (kinda like a fork), there are some conflicts that users will run into when they install WebGPU in an app that already has Nitro Modules installed (or other way around).

An official full fix would be to migrate WebGPU to Nitro, not only for better maintenance, but also for better performance and stability. I really don't think the migration is a huge effort.

For now, this PR fixes the name of the Dispatcher that is injected into global, as Nitro uses the same name and when one of the two Nitro versions downcasts the global into the specific C++ symbol, we have conflics since it's two different C++ symbols - it's either nitro::margelo::Dispatcher (the official one) or the WebGPU margelo::Dispatcher.

It's essentially a race condition with no clear error log since its just a C++ pointer cast that fails (super hard to debug lol)

Fixes #270

[wcandillon]

@mrousavy should I also rename namespaces or it's not necessary?

[mrousavy]

nope not necessary for two reasons;

1. it's under margelo::, not margelo::nitro:: - so no conflicts i think.
2. even if there were conflicts, as long as it's linked completely separately the c++ compiler would mangle the names to avoid conflicts. if it's separate .so/dylibs.

[wcandillon]

Thanks a lot!