[WIP] [PATCH] ldb: new on-disk pack format

[Aaron Haslett]

Garming discovered poor performance when recursively calculating group
membership for a user during LDAP bind.  This WIP patch attempts to fix
the problem by separating values from the rest of the data in our LDB
pack format.  This should dramatically reduce the amount of data loaded
into cache while unpacking with flag LDB_UNPACK_DATA_FLAG_NO_DATA_ALLOC.

Correctness testing is included and a CI run is here:

https://gitlab.com/samba-team/devel/samba/pipelines/59051539

To be done:

  * Performance testing
  * Research into OpenLDAP's pack format and possible modifications to
    ours based on theirs


Thanks :)

Aaron H.