[parser] Lift template literal invalid escape restriction

src/flag-definitions.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file defines all of the flags.  It is separated into different section,
 // for Debug, Release, Logging and Profiling, etc.  To add a new flag, find the
 // correct section, and use one of the DEFINE_ macros, without a trailing ';'.
 //
 // This include does not have a guard, because it is a template-style include,
 // which can be included multiple times in different modes.  It expects to have
@@ skipping 191 matching lines @@
   V(harmony_do_expressions, "harmony do-expressions")                   \
   V(harmony_regexp_named_captures, "harmony regexp named captures")     \
   V(harmony_regexp_property, "harmony unicode regexp property classes") \
   V(harmony_function_tostring, "harmony Function.prototype.toString")   \
   V(harmony_class_fields, "harmony public fields in class literals")    \
   V(harmony_async_iteration, "harmony async iteration")                 \
   V(harmony_dynamic_import, "harmony dynamic import")                   \
   V(harmony_promise_finally, "harmony Promise.prototype.finally")
 
 // Features that are complete (but still behind --harmony/es-staging flag).
-#define HARMONY_STAGED(V)                                   \
-  V(harmony_regexp_lookbehind, "harmony regexp lookbehind") \
-  V(harmony_restrictive_generators,                         \
-    "harmony restrictions on generator declarations")       \
-  V(harmony_object_rest_spread, "harmony object rest spread properties")
+#define HARMONY_STAGED(V)                                                \
+  V(harmony_regexp_lookbehind, "harmony regexp lookbehind")              \
+  V(harmony_restrictive_generators,                                      \
+    "harmony restrictions on generator declarations")                    \
+  V(harmony_object_rest_spread, "harmony object rest spread properties") \
+  V(harmony_template_escapes,                                            \
+    "harmony invalid escapes in tagged template literals")
 
 // Features that are shipping (turned on by default, but internal flag remains).
 #define HARMONY_SHIPPING_BASE(V) \
   V(harmony_trailing_commas,     \
     "harmony trailing commas in function parameter lists")
 
 #ifdef V8_I18N_SUPPORT
 #define HARMONY_SHIPPING(V)                                        \
   HARMONY_SHIPPING_BASE(V)                                         \
   V(datetime_format_to_parts, "Intl.DateTimeFormat.formatToParts") \
@@ skipping 1070 matching lines @@
 #undef DEFINE_ALIAS_FLOAT
 #undef DEFINE_ALIAS_ARGS
 
 #undef FLAG_MODE_DECLARE
 #undef FLAG_MODE_DEFINE
 #undef FLAG_MODE_DEFINE_DEFAULTS
 #undef FLAG_MODE_META
 #undef FLAG_MODE_DEFINE_IMPLICATIONS
 
 #undef COMMA