Make necessary changes to updateRelationshipsResponder and updateRelationships to support RelationshipRequest which is union of previous TraditionalRelationshipRequest and FarcasterRelationshipRequest.

• Using request.action instead of destructuring makes it clear to flow in request.action === relationshipActions.FARCASTER_MUTUAL branch that request.userIDsToFID is available
• We get userIDs using userIDsToFID if farcaster request and pass to new Set(requestUserIDs) which is the only place request.userIDs is "directly" consumed

Depends on D11610

Send both traditional and farcaster requests, set breakpoint in updateRelationships, ensure that values are as expected at each step.