[MergedRoomCreationItem] DM: RoomDescriptionText use the roomName instead of memberName

### Steps to reproduce

Steps to reproduce
Create a DM with someone and update the name of the room.
The room description text will use the room name instead of the other member name.

### Outcome

We should use data.memberName instead roomSummary?.displayName

### Your phone model

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### Operating system version

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### Application version

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### Homeserver

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### Will you send logs?

No

Locate the MergedRoomCreationItem implementation and inspect how its RoomDescriptionText is built, focusing on data.memberName and roomSummary?.displayName. Reproduce the direct-message room rename scenario described in the issue, then verify that the description continues to show the other member's name rather than the renamed room name.

Written by the indexing model from the issue text.