Integrate latest core changes

[nesium]

New/updated JS API:

export interface RoomBase {
  // …
  loadComposingUsers(): Promise<ParticipantBasicInfo[]>;
  // …
}

export class Avatar {
  /**
  * An opaque identifier to check if the contents of the `Avatar` have changed.
  * While `ProseClient` caches loaded avatars, checking for a change in the `Avatar` might
  * still make sense, since `Client::loadAvatarDataURL` is asynchronous.
  */
  readonly id: string;
}

export class JabberClient {
  toString(): string;
  isProse(): boolean;
}

export class UserBasicInfo {
  // …
  readonly avatar: Avatar | undefined;
  // …
}

export class UserPresenceInfo {
  // …
  readonly avatar: Avatar | undefined;
  /**
  * XEP-0108: User Activity
  */
  readonly status: UserStatus | undefined;
  /**
  * Contains the full name only if first and last name are set.
  */
  readonly fullName: string | undefined;
  // …
}

export class ParticipantId {
  toString(): string;
}

export class ParticipantBasicInfo {
  readonly avatar: Avatar | undefined;
  readonly id: ParticipantId;
  readonly name: string;
}

export class ParticipantInfo {
  // …
  readonly avatar: Avatar | undefined;
  readonly client: JabberClient | undefined;
  readonly id: ParticipantId;
  /**
  * XEP-0310: Presence State Annotations
  */
  readonly status: string | undefined;
  // …
}

export class Contact {
  // …
  /**
  * Contains the full name only if first and last name are set.
  */
  readonly fullName: string | undefined;
  // …
}

export class ProseClient {
  // …
/**
* XEP-0084: User Avatar
* https://xmpp.org/extensions/xep-0084.html
* @param {Avatar} avatar
* @returns {Promise<string | undefined>}
*/
  loadAvatarDataURL(avatar: Avatar): Promise<string | undefined>;
  // …
}