Add companion `Key`s to `GroupImage`, `FriendImage`, `OnlineImage`, `OfflineImage`

mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/Image.kt

@@ -85,6 +85,8 @@ abstract class AbstractImage internal constructor() : Image {
  * 一般由 [Contact.uploadImage] 得到
  */
 interface OnlineImage : Image {
+    companion object Key : Message.Key<OnlineImage>
+
     /**
      * 原图下载链接. 包含域名
      */
@@ -115,7 +117,9 @@ suspend fun Image.queryUrl(): String {
  * 一般由 [Contact.uploadImage] 得到
  * @see queryOriginUrl
  */
-interface OfflineImage : Image
+interface OfflineImage : Image {
+    companion object Key : Message.Key<OfflineImage>
+}
 
 /**
  * 原图下载链接. 包含域名
@@ -142,6 +146,8 @@ suspend inline fun OfflineImage.queryOriginUrl(): String = queryUrl()
 // CustomFace
 @OptIn(MiraiInternalAPI::class)
 sealed class GroupImage : AbstractImage() {
+    companion object Key : Message.Key<GroupImage>
+
     abstract val filepath: String
     abstract val fileId: Int
     abstract val serverIp: Int
@@ -213,6 +219,8 @@ abstract class OnlineGroupImage : GroupImage(), OnlineImage
  */ // NotOnlineImage
 @OptIn(MiraiInternalAPI::class)
 sealed class FriendImage : AbstractImage() {
+    companion object Key : Message.Key<FriendImage>
+
     abstract val resourceId: String
     abstract val md5: ByteArray
     abstract val filepath: String

mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/MessageChain.kt

@@ -127,6 +127,10 @@ fun <M : Message> MessageChain.firstOrNull(key: Message.Key<M>): M? = when (key)
     AtAll -> first<AtAll>()
     PlainText -> first<PlainText>()
     Image -> first<Image>()
+    OnlineImage -> first<OnlineImage>()
+    OfflineImage -> first<OfflineImage>()
+    GroupImage -> first<GroupImage>()
+    FriendImage -> first<FriendImage>()
     Face -> first<Face>()
     QuoteReply -> first<QuoteReply>()
     MessageSource -> first<MessageSource>()
@@ -360,7 +364,7 @@ fun Message.flatten(): Sequence<SingleMessage> {
 }
 
 fun CombinedMessage.flatten(): Sequence<SingleMessage> {
-    if (this.isFlat()){
+    if (this.isFlat()) {
         @Suppress("UNCHECKED_CAST")
         return (this as Iterable<SingleMessage>).asSequence()
     } else return this.asSequence().flatten()