LibJS: GC should gather roots from all active interpreters

If we are in a nested execution context, we shouldn't only mark things
used by the active interpreter.

Libraries/LibJS/Heap/Heap.cpp

@@ -105,9 +105,7 @@ void Heap::collect_garbage(CollectionType collection_type, bool print_report)
 
 void Heap::gather_roots(HashTable<Cell*>& roots)
 {
-    if (auto* interpreter = vm().interpreter_if_exists())
-        interpreter->gather_roots({}, roots);
-
+    vm().gather_roots(roots);
     gather_conservative_roots(roots);
 
     for (auto* handle : m_handles)

Libraries/LibJS/Interpreter.cpp

@@ -223,7 +223,7 @@ Symbol* Interpreter::get_global_symbol(const String& description)
     return new_global_symbol;
 }
 
-void Interpreter::gather_roots(Badge<Heap>, HashTable<Cell*>& roots)
+void Interpreter::gather_roots(HashTable<Cell*>& roots)
 {
     roots.set(m_exception);
 

Libraries/LibJS/Interpreter.h

@@ -135,7 +135,7 @@ public:
 
     Symbol* get_global_symbol(const String& description);
 
-    void gather_roots(Badge<Heap>, HashTable<Cell*>&);
+    void gather_roots(HashTable<Cell*>&);
 
     void enter_scope(const ScopeNode&, ArgumentVector, ScopeType, GlobalObject&);
     void exit_scope(const ScopeNode&);

Libraries/LibJS/Runtime/VM.cpp

@@ -82,4 +82,10 @@ VM::InterpreterScope::~InterpreterScope()
     m_interpreter.vm().pop_interpreter(m_interpreter);
 }
 
+void VM::gather_roots(HashTable<Cell*>& roots)
+{
+    for (auto* interpreter : m_interpreters)
+        interpreter->gather_roots(roots);
+}
+
 }

Libraries/LibJS/Runtime/VM.h

@@ -53,6 +53,8 @@ public:
         Interpreter& m_interpreter;
     };
 
+    void gather_roots(HashTable<Cell*>&);
+
 private:
     VM();