test-js: Add global function to determine if using bytecode interpreter

This is intended to be used in adding test-js tests where there is
different behaviour between the AST interpreter and bytecode mode.
In particular, this is useful for tests which fail in AST, but pass in
bytecode, as the AST interpreter is run in CI but bytecode is not.

Tests/LibJS/test-js.cpp

@@ -12,6 +12,11 @@ TEST_ROOT("Userland/Libraries/LibJS/Tests");
 
 TESTJS_PROGRAM_FLAG(test262_parser_tests, "Run test262 parser tests", "test262-parser-tests", 0);
 
+TESTJS_GLOBAL_FUNCTION(is_bytecode_interpreter_enabled, isBytecodeInterpreterEnabled, 0)
+{
+    return JS::Value(JS::Bytecode::Interpreter::enabled());
+}
+
 TESTJS_GLOBAL_FUNCTION(is_strict_mode, isStrictMode, 0)
 {
     return JS::Value(vm.in_strict_mode());