deps: V8: cherry-pick fbb28902e049

Original commit message:

    Update V8 postmortem metadata script

    This commit updates the gen-postmortem-metadata.py script to
    incorporate changes in V8 8.4. This removes the need to float a
    patch to the script in Node.js.

    Change-Id: I69da40e792f22748b0eee2952b9009b2f03d13f3
    Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2565275
    Reviewed-by: Joyee Cheung <[email protected]>
    Reviewed-by: Georg Neis <[email protected]>
    Commit-Queue: Joyee Cheung <[email protected]>
    Cr-Commit-Position: refs/heads/master@{#71646}

Refs: v8/v8@fbb2890

PR-URL: #36139
Reviewed-By: Jiawen Geng <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Myles Borins <[email protected]>
Reviewed-By: Shelley Vohr <[email protected]>

common.gypi

@@ -36,7 +36,7 @@
 
     # 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.11',
+    'v8_embedder_string': '-node.12',
 
     ##### V8 defaults for Node.js #####
 

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

@@ -287,6 +287,7 @@
     'SlicedString, offset, SMI, kOffsetOffset',
     'ThinString, actual, String, kActualOffset',
     'Symbol, name, Object, kDescriptionOffset',
+    'FixedArrayBase, length, SMI, kLengthOffset',
 ];
 
 #