Re: Shared detoast Datum proposal

Hi,

Here is a updated version, the main changes are:

1. an shared_detoast_datum.org file which shows the latest desgin and
pending items during discussion. 
2. I removed the slot->pre_detoast_attrs totally.
3. handle some pg_detoast_datum_slice use case.
4. Some implementation improvement.

commit 66c64c197a5dab97a563be5a291127e4c5d6841d (HEAD -> shared_detoast_value)
Author: yizhi.fzh <yizhi.fzh@alibaba-inc.com>
Date:   Sun Mar 3 13:48:25 2024 +0800

    shared detoast datum
    
    See the overall design & alternative design & testing in
    shared_detoast_datum.org

In the shared_detoast_datum.org, I added the alternative design part for
the idea of TOAST cache.

-- 
Best Regards
Andy Fan