Allocate `Realm` on the GC heap and store it in JsGlobal

[jameslahm]

I am working on implementing create intrinsics. I think JsGlobal could be stored in the realm. My opinion is that we could store realm and runtime in a context. And each time, runtime will first init, creating internal objects. And then context be created, storing runtime and init realm. Last, context can eval js code. WDYT?

[playXE]

We still should have an access to runtime and realm instance from global object. That's what JavaScriptCore has too

[jameslahm]

That also makes sense. So we also add runtimeRef and realmRef in JsGlobal? WDYT?

[playXE]

So we also add runtimeRef and realmRef in JsGlobal?

Yep