Use ijson to parse the response to /send_join, reducing memory usage. (#9958)

Instead of parsing the full response to `/send_join` into Python objects (which can be huge for large rooms) and *then* parsing that into events, we instead use ijson to stream parse the response directly into `EventBase` objects.

synapse/http/client.py

@@ -813,7 +813,12 @@ class _ReadBodyWithMaxSizeProtocol(protocol.Protocol):
         if self.deferred.called:
             return
 
-        self.stream.write(data)
+        try:
+            self.stream.write(data)
+        except Exception:
+            self.deferred.errback()
+            return
+
         self.length += len(data)
         # The first time the maximum size is exceeded, error and cancel the
         # connection. dataReceived might be called again if data was received