Ship RegExp Unicode property escapes

Intent to ship:
https://groups.google.com/d/msg/v8-users/isa2JrstEbE/i6UvFO7RBwAJ

BUG=v8:4743

Change-Id: I62cdc6fa1f114fc8be26c5cf354c45a15ce49ab7
Reviewed-on: https://chromium-review.googlesource.com/761776
Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Mathias Bynens <mathias@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49312}

src/flag-definitions.h

@@ -203,23 +203,23 @@ DEFINE_IMPLICATION(harmony_import_meta, harmony_dynamic_import)
// Features that are complete (but still behind --harmony/es-staging flag).
#define HARMONY_STAGED(V)                                               \
  V(harmony_function_tostring, "harmony Function.prototype.toString")   \
  V(harmony_regexp_property, "harmony Unicode regexp property classes") \
  V(harmony_restrict_constructor_return,                                \
    "harmony disallow non undefined primitive return value from class " \
    "constructor")                                                      \
  V(harmony_dynamic_import, "harmony dynamic import")

// Features that are shipping (turned on by default, but internal flag remains).
#define HARMONY_SHIPPING_BASE(V)                                         \
  V(harmony_strict_legacy_accessor_builtins,                             \
    "treat __defineGetter__ and related functions as strict")            \
  V(harmony_sharedarraybuffer, "harmony sharedarraybuffer")              \
  V(harmony_regexp_dotall, "harmony regexp dotAll flag")                 \
  V(harmony_regexp_lookbehind, "harmony regexp lookbehind")              \
  V(harmony_regexp_named_captures, "harmony regexp named captures")      \
  V(harmony_async_iteration, "harmony async iteration")                  \
  V(harmony_template_escapes,                                            \
    "harmony invalid escapes in tagged template literals")               \
#define HARMONY_SHIPPING_BASE(V)                                        \
  V(harmony_strict_legacy_accessor_builtins,                            \
    "treat __defineGetter__ and related functions as strict")           \
  V(harmony_sharedarraybuffer, "harmony sharedarraybuffer")             \
  V(harmony_regexp_dotall, "harmony regexp dotAll flag")                \
  V(harmony_regexp_lookbehind, "harmony regexp lookbehind")             \
  V(harmony_regexp_named_captures, "harmony regexp named captures")     \
  V(harmony_regexp_property, "harmony Unicode regexp property classes") \
  V(harmony_async_iteration, "harmony async iteration")                 \
  V(harmony_template_escapes,                                           \
    "harmony invalid escapes in tagged template literals")              \
  V(harmony_promise_finally, "harmony Promise.prototype.finally")

#ifdef V8_INTL_SUPPORT