test: update postmortem metadata test for V8 7.6

The following metadata has changed:

- v8dbg_class_FixedTypedArrayBase__base_pointer__Object
  - Field moved from FixedTypedArrayBase to JSTypedArray.
  - Postmortem tools should use v8dbg_class_JSTypedArray__base_pointer__Object.
  - Refs: v8/v8@70bd7cf

- v8dbg_class_FixedTypedArrayBase__external_pointer__uintptr_t
  - Field moved from FixedTypedArrayBase to JSTypedArray.
  - Add new constant: v8dbg_class_JSTypedArray__external_pointer__uintptr_t
  - Refs: v8/v8@70bd7cf

- v8dbg_class_Map__instance_descriptors_offset
  - Underlying constant was renamed to kInstanceDescriptorsOffset.
  - Postmortem tools should not need to update anything for this constant.
  - Refs: v8/v8@15a7e04

PR-URL: #28016
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Refael Ackermann (רפאל פלחי) <refack@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>

test/v8-updates/test-postmortem-metadata.js

@@ -66,8 +66,8 @@ function getExpectedSymbols() {
     'v8dbg_class_ConsString__second__String',
     'v8dbg_class_FixedArray__data__uintptr_t',
     'v8dbg_class_FixedArrayBase__length__SMI',
-    'v8dbg_class_FixedTypedArrayBase__base_pointer__Object',
-    'v8dbg_class_FixedTypedArrayBase__external_pointer__uintptr_t',
+    'v8dbg_class_JSTypedArray__base_pointer__Object',
+    'v8dbg_class_JSTypedArray__external_pointer__uintptr_t',
     'v8dbg_class_HeapNumber__value__double',
     'v8dbg_class_HeapObject__map__Map',
     'v8dbg_class_JSArray__length__Object',