Implement [[HostDefined]] for Module and Script

[jedel1043]

We left the implementation of [[HostDefined]] fields for Script and Module as a future improvement, but it's pretty necessary for users that want to store additional data on a runnable.

Script:

boa/boa_engine/src/script.rs

Lines 45 to 53 in 348c757

	#[derive(Trace, Finalize)]
	struct Inner {
	realm: Realm,
	#[unsafe_ignore_trace]
	source: boa_ast::Script,
	codeblock: GcRefCell<Option<Gc<CodeBlock>>>,
	loaded_modules: GcRefCell<FxHashMap<JsString, Module>>,
	host_defined: (),
	}

Module:

boa/boa_engine/src/module/mod.rs

Lines 284 to 291 in 348c757

	#[derive(Trace, Finalize)]
	struct Inner {
	realm: Realm,
	environment: GcRefCell<Option<Gc<DeclarativeEnvironment>>>,
	namespace: GcRefCell<Option<JsObject>>,
	kind: ModuleKind,
	host_defined: (),
	}

Probably a simple GcRefCell<Box<dyn NativeObject>> and an accessor/mutable accessor should be enough for both.

[arexon]

I'm willing to work on this.

Probably a simple GcRefCell<Box> and an accessor/mutable accessor should be enough for both.

Wouldn't this use HostDefined struct? Or is [[HostDefined]] meant to store only 1 object in Script and Module?

[jedel1043]

Wouldn't this use HostDefined struct? Or is [[HostDefined]] meant to store only 1 object in Script and Module?

Both are good. We can implement it using HostDefined for now and if there's not much usage for storing multiple objects, we can just return to a simple Box<dyn NativeObject>.