LibJS: Add host layering point related to modules to VM

Also make HostResolveImportedModule fail on the browser to prevent
module loading for now.

Userland/Libraries/LibJS/Forward.h

@@ -170,6 +170,7 @@ class Script;
 class Shape;
 class Statement;
 class StringOrSymbol;
+class SourceTextModule;
 class Symbol;
 class Token;
 class Utf16String;
@@ -180,6 +181,7 @@ class WrappedFunction;
 enum class DeclarationKind;
 struct AlreadyResolved;
 struct JobCallback;
+struct ModuleRequest;
 struct PromiseCapability;
 
 // Not included in JS_ENUMERATE_NATIVE_OBJECTS due to missing distinct prototype

Userland/Libraries/LibJS/Runtime/VM.h

@@ -241,6 +241,13 @@ public:
 
     ScriptOrModule get_active_script_or_module() const;
 
+    Function<ThrowCompletionOr<NonnullRefPtr<Module>>(ScriptOrModule, ModuleRequest const&)> host_resolve_imported_module;
+    Function<void(ScriptOrModule, ModuleRequest const&, PromiseCapability)> host_import_module_dynamically;
+    Function<void(ScriptOrModule, ModuleRequest const&, PromiseCapability, Promise*)> host_finish_dynamic_import;
+
+    Function<HashMap<PropertyKey, Value>(SourceTextModule const&)> host_get_import_meta_properties;
+    Function<void(Object*, SourceTextModule const&)> host_finalize_import_meta;
+
 private:
     explicit VM(OwnPtr<CustomData>);
 

Userland/Libraries/LibWeb/Bindings/MainThreadVM.cpp

@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <LibJS/Module.h>
 #include <LibJS/Runtime/VM.h>
 #include <LibWeb/Bindings/MainThreadVM.h>
 
@@ -15,6 +16,10 @@ JS::VM& main_thread_vm()
     if (!vm) {
         vm = JS::VM::create(make<WebEngineCustomData>());
         static_cast<WebEngineCustomData*>(vm->custom_data())->event_loop.set_vm(*vm);
+
+        vm->host_resolve_imported_module = [&](JS::ScriptOrModule, JS::ModuleRequest const&) -> JS::ThrowCompletionOr<NonnullRefPtr<JS::Module>> {
+            return vm->throw_completion<JS::InternalError>(vm->current_realm()->global_object(), JS::ErrorType::NotImplemented, "Modules in the browser");
+        };
     }
     return *vm;
 }