deps: V8: cherry-pick a7dffcd767be

Original commit message:

    [postmortem] Load files using utf-8 to support Python 3

    Change-Id: I174d38cc33210c07d1a7596627e1b2d21bb06313
    Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1895560
    Reviewed-by: Mathias Bynens <mathias@chromium.org>
    Commit-Queue: Michaël Zasso <mic.besace@gmail.com>
    Cr-Commit-Position: refs/heads/master@{#64717}

Refs: v8/v8@a7dffcd

PR-URL: #30218
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>

common.gypi

@@ -38,7 +38,7 @@
 
     # Reset this number to 0 on major V8 upgrades.
     # Increment by one for each non-official patch applied to deps/v8.
-    'v8_embedder_string': '-node.15',
+    'v8_embedder_string': '-node.16',
 
     ##### V8 defaults for Node.js #####
 

deps/v8/tools/gen-postmortem-metadata.py

@@ -49,6 +49,7 @@
 # for py2/py3 compatibility
 from __future__ import print_function
 
+import io
 import re
 import sys
 
@@ -380,7 +381,7 @@ def load_objects():
 
 
 def load_objects_from_file(objfilename, checktypes):
-        objfile = open(objfilename, 'r');
+        objfile = io.open(objfilename, 'r', encoding='utf-8');
         in_insttype = False;
 
         typestr = '';
@@ -575,7 +576,7 @@ def load_fields():
 
 
 def load_fields_from_file(filename):
-        inlfile = open(filename, 'r');
+        inlfile = io.open(filename, 'r', encoding='utf-8');
 
         #
         # Each class's fields and the corresponding offsets are described in the