message: edit message can now have files
diff: import { Embed } from "../embeds/embed.ts";
  +import { FileContent } from "../misc/file_content.ts";
  import { AllowedMentions } from "./allowed_mentions.ts";
  import { Attachment } from "./attachment.ts";
  @@ -10,6 +11,8 @@ export interface EditMessage {
  embed?: Embed | null;
  /** Edit the flags of the message (only `SUPRESS_EMBEDS` can currently be set/unset) */
  flags?: 4 | null;
  + /** The contents of the file being sent/edited */
  + file?: FileContent | FileContent[] | null;
  /** Allowed mentions for the message */
  allowedMentions?: AllowedMentions | null;
  /** Attached files to keep */
  