And receives in its constructor the enginehost and registry. This simplifies the creation
of the NodeWorkflow, or later on the Google3Workflow etc, since all the duplicate logic
is now in a single base class.
This is yak shaving for internal stuff.
This should clean up the code a bit.
Note: at first I added the no-useless-cast rule, but after getting frustrated
with it (as it has many false positive), I decided to remove the rule but some
useless casts were removed so I let those in the PR.
