WIP: Feature: Fast forward content streams during rebase (Made non breaking)

[mhsdesign]

depends on #5735
fundament later for #5771

as elaborated here #5264 (comment)
there is a dilemma to be solved. As we didn't put the fast forward event into the Neos betas at that time, half a year before the release we now have to find a way to implement fast forwarding non breaking with the events we have.
My primary goal was to keep the WorkspaceWasRebased event as is meaning that we require the previous content stream id and a new content stream id. That is achieved internally by just moving the internal pointer from old to new. But moving a content stream like this now looks very weird on the events as one event affects now the outcome of two streams which is not the intention.

Maybe the outcome is that we do still want new events and be a little breaking for 9.2, i could for example for catchup hooks and simple projections imagine an marker interface like WorkspaceNewContentInterface which can simply implemented by the WorkspaceWasRebased event as well as a WorkspaceWasForwarded event to denote that any data build up sofar must be reevaluated.

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• Code follows the PSR-2 coding style
• Tests have been created, run and adjusted as needed
• The PR is created against the correct branch:
  • If it's a bugfix, use the lowest maintained branch which has the bug
  • If it's a non-breaking feature, use the branch of the next version (might be either minor or major)
  • If it's a breaking feature it should typically go into the next major version
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