LibJS: Add a new EnterScope bytecode instruction

This is intended to perform the same duties as enter_scope() does in
the AST tree-walk interpreter:

- Hoisted function declaration processing
- Hoisted variable declaration processing
- ... maybe more

This first cut only implements the function declaration processing.

Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp

@@ -20,6 +20,7 @@ Optional<Bytecode::Register> ASTNode::generate_bytecode(Bytecode::Generator&) co
 
 Optional<Bytecode::Register> ScopeNode::generate_bytecode(Bytecode::Generator& generator) const
 {
+    generator.emit<Bytecode::Op::EnterScope>(*this);
     for (auto& child : children()) {
         [[maybe_unused]] auto reg = child.generate_bytecode(generator);
     }