Breakout rooms mixed up in participants editor

[Antreesy]

Technically, only names could be mixed up, though still confusing. Could happen because of different sorting order of room tokens (2 goes before 1 in alphabetic order).

• Sort rooms by display names, not by token
• Don't calculate display names manually, use provided by server:
  

  spreed/src/components/BreakoutRoomsEditor/BreakoutRoomsParticipantsEditor.vue

  Lines 33 to 43 in 09fadad

  	<template v-for="(item, index) in assignments">
  	<BreakoutRoomItem :key="index"
  	class="participants-editor__section"
  	:name="roomName(index)">
  	<SelectableParticipant v-for="attendeeId in item"
  	:key="attendeeId"
  	:value="assignments"
  	:checked.sync="selectedParticipants"
  	:participant="attendeesById[attendeeId]" />
  	</BreakoutRoomItem>
  	</template>

Originally posted by @DorraJaouad in #11649 (review)