Refactor user directory tests (#10935)

* Pull out GetUserDirectoryTables helper
* Don't rebuild the dir in tests that don't need it

In #10796 I changed registering a user to add directory entries under.
This means we don't have to force a directory regbuild in to tests of
the user directory search.

* Move test_initial to tests/storage
* Add type hints to both test_user_directory files

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

tests/unittest.py

@@ -28,6 +28,7 @@ from canonicaljson import json
 from twisted.internet.defer import Deferred, ensureDeferred, succeed
 from twisted.python.failure import Failure
 from twisted.python.threadpool import ThreadPool
+from twisted.test.proto_helpers import MemoryReactor
 from twisted.trial import unittest
 from twisted.web.resource import Resource
 
@@ -46,6 +47,7 @@ from synapse.logging.context import (
 )
 from synapse.server import HomeServer
 from synapse.types import UserID, create_requester
+from synapse.util import Clock
 from synapse.util.httpresourcetree import create_resource_tree
 from synapse.util.ratelimitutils import FederationRateLimiter
 
@@ -371,7 +373,7 @@ class HomeserverTestCase(TestCase):
 
         return config
 
-    def prepare(self, reactor, clock, homeserver):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, homeserver: HomeServer):
         """
         Prepare for the test.  This involves things like mocking out parts of
         the homeserver, or building test data common across the whole test