Avoid using fixture method in production code.

libraries/matrix/api/src/main/kotlin/io/element/android/libraries/matrix/api/room/RoomMember.kt

@@ -17,6 +17,7 @@
 package io.element.android.libraries.matrix.api.room
 
 import io.element.android.libraries.matrix.api.core.UserId
+import io.element.android.libraries.matrix.api.user.MatrixUser
 
 data class RoomMember(
     val userId: UserId,
@@ -78,3 +79,10 @@ enum class RoomMembershipState {
 fun RoomMember.getBestName(): String {
     return displayName?.takeIf { it.isNotEmpty() } ?: userId.value
 }
+
+fun RoomMember.toMatrixUser() = MatrixUser(
+    userId = userId,
+    displayName = displayName,
+    avatarUrl = avatarUrl,
+)
+