Docs: https://docs.google.com/document/d/13n1qaB6A-gvgWc9NDhWm-UPuOqow_Y0DNgCeTbtIotI

Modify that C++ backend so that it can emit either runtime C++ or
postmortem debugging code. When in postmortem debugging mode, the
overall code structure would look similar with some difference:
1. Instead of passing an Isolate* everywhere, we pass a MemoryAccessor.
2. Instead of runtime class names like String, we use uintptr_t
3. When loading data from objects, instead of TaggedField<T>::load or
Object::ReadField (which read from the current process), we use the
MemoryAccessor and read data from the debuggee process.
4. Return values should be wrapped in the Value struct.

Implement the debug accessors for complex length expressions and add
test for such class (SmallOrderedHashSet).

Change-Id: I34107c92b31ed4e07bb628ae58c84487e41ba648
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2477921
Commit-Queue: Z Nguyen-Huu <duongn@microsoft.com>
Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Seth Brenith <seth.brenith@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#72148}