Move device changes off the main process (#18581)

The main goal of this PR is to handle device list changes onto multiple
writers, off the main process, so that we can have logins happening
whilst Synapse is rolling-restarting.

This is quite an intrusive change, so I would advise to review this
commit by commit; I tried to keep the history as clean as possible.

There are a few things to consider:

- the `device_list_key` in stream tokens becomes a
`MultiWriterStreamToken`, which has a few implications in sync and on
the storage layer
- we had a split between `DeviceHandler` and `DeviceWorkerHandler` for
master vs. worker process. I've kept this split, but making it rather
writer vs. non-writer worker, using method overrides for doing
replication calls when needed
- there are a few operations that need to happen on a single worker at a
time. Instead of using cross-worker locks, for now I made them run on
the first writer on the list

---------

Co-authored-by: Eric Eastwood <erice@element.io>

synapse/module_api/__init__.py

@@ -66,7 +66,6 @@ from synapse.handlers.auth import (
     ON_LOGGED_OUT_CALLBACK,
     AuthHandler,
 )
-from synapse.handlers.device import DeviceHandler
 from synapse.handlers.push_rules import RuleSpec, check_actions
 from synapse.http.client import SimpleHttpClient
 from synapse.http.server import (
@@ -925,8 +924,6 @@ class ModuleApi:
     ) -> Generator["defer.Deferred[Any]", Any, None]:
         """Invalidate an access token for a user
 
-        Can only be called from the main process.
-
         Added in Synapse v0.25.0.
 
         Args:
@@ -939,10 +936,6 @@ class ModuleApi:
         Raises:
             synapse.api.errors.AuthError: the access token is invalid
         """
-        assert isinstance(self._device_handler, DeviceHandler), (
-            "invalidate_access_token can only be called on the main process"
-        )
-
         # see if the access token corresponds to a device
         user_info = yield defer.ensureDeferred(
             self._auth.get_user_by_access_token(access_token)