LibJS/Bytecode: Defer GetGlobal identifier lookup until cache misses

This way we avoid looking up the identifier when the cache hits.

Userland/Libraries/LibJS/Bytecode/CommonImplementations.h

@@ -231,7 +231,7 @@ inline ThrowCompletionOr<Value> get_by_value(VM& vm, Optional<DeprecatedFlyStrin
     return TRY(object->internal_get(property_key, base_value));
 }
 
-inline ThrowCompletionOr<Value> get_global(Bytecode::Interpreter& interpreter, DeprecatedFlyString const& identifier, GlobalVariableCache& cache)
+inline ThrowCompletionOr<Value> get_global(Interpreter& interpreter, IdentifierTableIndex identifier_index, GlobalVariableCache& cache)
 {
     auto& vm = interpreter.vm();
     auto& binding_object = interpreter.global_object();
@@ -246,6 +246,8 @@ inline ThrowCompletionOr<Value> get_global(Bytecode::Interpreter& interpreter, D
 
     cache.environment_serial_number = declarative_record.environment_serial_number();
 
+    auto& identifier = interpreter.current_executable().get_identifier(identifier_index);
+
     if (vm.running_execution_context().script_or_module.has<NonnullGCPtr<Module>>()) {
         // NOTE: GetGlobal is used to access variables stored in the module environment and global environment.
         //       The module environment is checked first since it precedes the global environment in the environment chain.

Userland/Libraries/LibJS/Bytecode/Interpreter.cpp

@@ -1264,7 +1264,7 @@ ThrowCompletionOr<void> GetCalleeAndThisFromEnvironment::execute_impl(Bytecode::
 
 ThrowCompletionOr<void> GetGlobal::execute_impl(Bytecode::Interpreter& interpreter) const
 {
-    interpreter.set(dst(), TRY(get_global(interpreter, interpreter.current_executable().get_identifier(m_identifier), interpreter.current_executable().global_variable_caches[m_cache_index])));
+    interpreter.set(dst(), TRY(get_global(interpreter, m_identifier, interpreter.current_executable().global_variable_caches[m_cache_index])));
     return {};
 }