deps: V8: cherry-pick b38dfaf3a633

Original commit message:

    [postmortem] update Symbol and *String metadata

    Symbol and *String classes are now declared on Torque with
    generateCppClass, which means they don't use macro accessors anymore. As
    such, the gen-postmortem-metadata script is not able to automatically
    detect fields for those classes. Define metadata for those fields
    manually for now. In the future we might want to generate it from Torque
    for consistency.

    Also renamed a few *String fields metadata to match the expected format
    (className__fieldName__fieldType). For more context:
    nodejs/llnode#287 (comment).

    R=bmeurer@chromium.org, hpayer@chromium.org, verwaest@chromium.org, yangguo@chromium.org

    Change-Id: I82fe8315cdbfd1b8c64c6a8d5dc011b1edaec39e
    Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1847783
    Reviewed-by: Toon Verwaest <verwaest@chromium.org>
    Commit-Queue: Toon Verwaest <verwaest@chromium.org>
    Cr-Commit-Position: refs/heads/master@{#64313}

Refs: v8/v8@b38dfaf
PR-URL: #30870
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.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.28',
+    'v8_embedder_string': '-node.29',
 
     ##### V8 defaults for Node.js #####
 

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

@@ -230,15 +230,6 @@
 
     { 'name': 'class_SharedFunctionInfo__function_data__Object',
         'value': 'SharedFunctionInfo::kFunctionDataOffset' },
-
-    { 'name': 'class_ConsString__first_offset__int',
-        'value': 'ConsString::kFirstOffset' },
-    { 'name': 'class_ConsString__second_offset__int',
-        'value': 'ConsString::kSecondOffset' },
-    { 'name': 'class_SlicedString__offset_offset__int',
-        'value': 'SlicedString::kOffsetOffset' },
-    { 'name': 'class_ThinString__actual_offset__int',
-        'value': 'ThinString::kActualOffset' },
 ];
 
 #
@@ -287,6 +278,11 @@
     'Code, instruction_size, int, kInstructionSizeOffset',
     'String, length, int32_t, kLengthOffset',
     'DescriptorArray, header_size, uintptr_t, kHeaderSize',
+    'ConsString, first, String, kFirstOffset',
+    'ConsString, second, String, kSecondOffset',
+    'SlicedString, offset, SMI, kOffsetOffset',
+    'ThinString, actual, String, kActualOffset',
+    'Symbol, name, Object, kNameOffset',
 ];
 
 #