Due to the fact that roles may be instantiated with different sets of
params (multiple inclusions of the same role or via role dependencies),
simply tracking notified handlers by name does not work. This patch
changes the way we track handler notifications by using the handler
object itself instead of just the name, allowing for multiple internal
instances. Normally this would be bad, but we also modify the way we
search for handlers by first looking at the notifying tasks dependency
chain (ensuring that roles find their own handlers first) and then at
the main list of handlers, using the first match it finds.
This patch also modifies the way we setup the internal list of handlers,
which should allow us to correctly identify if a notified handler exists
more easily.
Fixes#15084
8218591fec