Optimise getting local members and membership counts (#3150)

The previous version was getting **ALL** membership events (as
`ClientEvents`, so going through `NewEventFromTrustedJSONWithID`) for a
given room.
Now we are querying only locally joined users as `ClientEvents`, which
should **significantly** reduce allocations.

Take for example a large room with 2k membership events, but only 1
local user - avoiding 1999 `NewEventFromTrustedJSONWithID` calls just to
calculate the `roomSize` which we can also query by other means.

This is also getting called for every `OutputRoomEvent` in the userAPI.

Benchmark with 1 local user and 100 remote users.
```
pkg: github.com/matrix-org/dendrite/userapi/consumers
cpu: 12th Gen Intel(R) Core(TM) i5-12500H
                    │   old.txt   │               new.txt               │
                    │   sec/op    │   sec/op     vs base                │
LocalRoomMembers-16   375.9µ ± 7%   327.6µ ± 6%  -12.85% (p=0.000 n=10)

                    │    old.txt    │               new.txt                │
                    │     B/op      │     B/op      vs base                │
LocalRoomMembers-16   79.426Ki ± 0%   8.507Ki ± 0%  -89.29% (p=0.000 n=10)

                    │   old.txt   │              new.txt               │
                    │  allocs/op  │ allocs/op   vs base                │
LocalRoomMembers-16   1015.0 ± 0%   277.0 ± 0%  -72.71% (p=0.000 n=10)
```
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Till 2023-07-13 14:19:08 +02:00 committed by GitHub
parent f12982472c
commit 5267cc0f54
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4 changed files with 109 additions and 19 deletions

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@ -227,6 +227,7 @@ type UserRoomserverAPI interface {
QueryMembershipsForRoom(ctx context.Context, req *QueryMembershipsForRoomRequest, res *QueryMembershipsForRoomResponse) error
PerformAdminEvacuateUser(ctx context.Context, userID string) (affected []string, err error)
PerformJoin(ctx context.Context, req *PerformJoinRequest) (roomID string, joinedVia spec.ServerName, err error)
JoinedUserCount(ctx context.Context, roomID string) (int, error)
}
type FederationRoomserverAPI interface {