feat(Partials): add DMChannel/MessageReaction#fetch() and Parti… (#3261)

* add DMChannel#fetch() & Action#getChannel({recipients})

* ref for MessageReaction partial

* typings

* add PartialTypes.REACTION

* accommodate for fully removed reactions

* fix incorrect wording and typo

* typings: MessageReaction#count is nullable

* typings: mark MessageReaction#partial as readonly

Co-Authored-By: Vlad Frangu <kingdgrizzle@gmail.com>

* fix(User): fetch dm channel if cached one is partial

* docs: add missing comma

Co-Authored-By: Antonio Román <kyradiscord@gmail.com>

src/client/actions/Action.js

@@ -36,6 +36,7 @@ class GenericAction {
     return data.channel || this.getPayload({
       id,
       guild_id: data.guild_id,
+      recipients: [data.author || { id: data.user_id }],
     }, this.client.channels, id, PartialTypes.CHANNEL);
   }
 
@@ -52,9 +53,9 @@ class GenericAction {
     const id = data.emoji.id || decodeURIComponent(data.emoji.name);
     return this.getPayload({
       emoji: data.emoji,
-      count: 0,
+      count: message.partial ? null : 0,
       me: user.id === this.client.user.id,
-    }, message.reactions, id, PartialTypes.MESSAGE);
+    }, message.reactions, id, PartialTypes.REACTION);
   }
 
   getMember(data, guild) {

src/client/actions/MessageReactionAdd.js

@@ -26,11 +26,8 @@ class MessageReactionAdd extends Action {
     if (!message) return false;
 
     // Verify reaction
-    const reaction = message.reactions.add({
-      emoji: data.emoji,
-      count: 0,
-      me: user.id === this.client.user.id,
-    });
+    const reaction = this.getReaction(data, message, user);
+    if (!reaction) return false;
     reaction._add(user);
     /**
      * Emitted whenever a reaction is added to a cached message.