test: update postmortem metadata test for V8 7.7

The following metadata has changed:

- v8dbg_class_ConsString__first__String
  - Class is now generated via torque.
  - Postmortem tools should use v8dbg_class_ConsString__first_offset__int
  - Refs: v8/v8@14274bb

- v8dbg_class_ConsString__second__String
  - Class is now generated via torque.
  - Postmortem tools should use v8dbg_class_ConsString__second_offset__int
  - Refs: v8/v8@14274bb

- v8dbg_class_SlicedString__offset__SMI
  - Class is now generated via torque.
  - Postmortem tools should use v8dbg_class_SlicedString__offset_offset__int
  - Refs: v8/v8@14274bb

- v8dbg_class_ThinString__actual__String
  - Class is now generated via torque.
  - Postmortem tools should use v8dbg_class_ThinString__actual_offset__int
  - Refs: v8/v8@14274bb

Backport-PR-URL: #29241
PR-URL: #28918
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

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

@@ -62,8 +62,8 @@ function getExpectedSymbols() {
     'v8dbg_bit_field3_number_of_own_descriptors_shift',
     'v8dbg_class_Code__instruction_size__int',
     'v8dbg_class_Code__instruction_start__uintptr_t',
-    'v8dbg_class_ConsString__first__String',
-    'v8dbg_class_ConsString__second__String',
+    'v8dbg_class_ConsString__first_offset__int',
+    'v8dbg_class_ConsString__second_offset__int',
     'v8dbg_class_FixedArray__data__uintptr_t',
     'v8dbg_class_FixedArrayBase__length__SMI',
     'v8dbg_class_JSTypedArray__base_pointer__Object',
@@ -104,10 +104,10 @@ function getExpectedSymbols() {
     'v8dbg_class_SharedFunctionInfo__name_or_scope_info__Object',
     'v8dbg_class_SharedFunctionInfo__script_or_debug_info__Object',
     'v8dbg_class_UncompiledData__start_position__int32_t',
-    'v8dbg_class_SlicedString__offset__SMI',
+    'v8dbg_class_SlicedString__offset_offset__int',
     'v8dbg_class_SlicedString__parent__String',
     'v8dbg_class_String__length__int32_t',
-    'v8dbg_class_ThinString__actual__String',
+    'v8dbg_class_ThinString__actual_offset__int',
     'v8dbg_context_idx_scope_info',
     'v8dbg_context_idx_prev',
     'v8dbg_context_min_slots',