[BUGFIX] Avoid dangling MM relations on workspace publish

When publishing workspace records with connected
"true" MM relations (uid_local / uid_foreign columns
and no TCA for that table), DataHandler triggers bugs:

* It updates uid_local or uid_foreign rows to negative
  uids during the process as intermediate DB state.
* It leaves "dangling" MM rows of the workspace record
  that has been pushed live.

The involved code is relatively well encapsulated,
it only kicks in for this "publish MM relations"
scenario, the impact of this patch is limited to
this area.

The patch rewrites MM workspace publish handling:

* Avoid parking state in a DataHandler class property
  only used in this scenario.
* Avoid moving a list of stateful RelationHandler
  instances around and dynamically calling methods
  on those instances.
* Avoid recursive flex form MM publish handling with
  indirect callback methods that change class state.
* Obsolete a RelationHandler method used only in
  this scenario.
* Reduce number of queries.

The result is a simplified, better encapsulated and well
commented solution. On a testing side, the patch brings
a scenario to verify flex form MM relation handling.
An according styleguide example is pending, too.

This patch allows us to change auto created MM table
definitions to unsigned uid_local and uid_foreign columns,
which is of course the right way to go.

Change-Id: I0d24f31cbd356f19937c2f8c18d432424e127b97
Resolves: #95275
Resolves: #81718
Releases: master
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/71097


Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>