Adds missing type hints to methods in the synapse.handlers
module and requires all methods to have type hints there.
This also removes the unused construct_auth_difference method
from the FederationHandler.
The full event content cannot be trusted from this API (as no auth
chain, etc.) is processed over federation. Returning the full event
content was a bug as MSC2946 specifies that only the stripped
state should be returned.
This also avoids calculating aggregations / annotations which go
unused.
This updates the ordering of the returned events from the spaces
summary API to that defined in MSC2946 (which updates MSC1772).
Previously a step was skipped causing ordering to be inconsistent with
clients.
