Update docs and OptIn annotations

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

@@ -12,10 +12,16 @@ package net.mamoe.mirai.message.data
 import net.mamoe.mirai.utils.MiraiExperimentalAPI
 import net.mamoe.mirai.utils.SinceMirai
 
+/**
+ * Json 消息.
+ *
+ * @see LightApp 一些消息实际上是 [LightApp]
+ */
 @SinceMirai("0.27.0")
 @OptIn(MiraiExperimentalAPI::class)
 class JsonMessage(override val content: String) : RichMessage {
     companion object Key : Message.Key<JsonMessage>
+
     // serviceId = 1
     override fun toString(): String = content
 }

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

@@ -13,7 +13,7 @@ import net.mamoe.mirai.utils.MiraiExperimentalAPI
 import net.mamoe.mirai.utils.SinceMirai
 
 /**
- * 小程序, 如音乐分享
+ * 小程序分享, 如音乐分享
  */
 @OptIn(MiraiExperimentalAPI::class)
 @SinceMirai("0.27.0")

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

@@ -9,18 +9,18 @@
 
 package net.mamoe.mirai.message.data
 
-import net.mamoe.mirai.utils.MiraiExperimentalAPI
 import net.mamoe.mirai.utils.SinceMirai
 
 /**
  * XML 消息等富文本消息
  *
  * @see XmlMessage
+ * @see JsonMessage
+ * @see LightApp
  */
 @SinceMirai("0.27.0")
 interface RichMessage : MessageContent {
     companion object Key : Message.Key<RichMessage>
 
-    @MiraiExperimentalAPI
     val content: String
 }