Avoid so much copypasta between 3PU and 3PL query by unifying around a ThirdPartyEntityKind enumeration

synapse/types.py

@@ -269,3 +269,10 @@ class RoomStreamToken(namedtuple("_StreamToken", "topological stream")):
             return "t%d-%d" % (self.topological, self.stream)
         else:
             return "s%d" % (self.stream,)
+
+
+# Some arbitrary constants used for internal API enumerations. Don't rely on
+# exact values; always pass or compare symbolically
+class ThirdPartyEntityKind(object):
+    USER = 'user'
+    LOCATION = 'location'