MM-11272 Added initial post metadata (#9175)

* MM-11272 Added app.PreparePostForClient

* MM-11272 Added app.PreparePostListForClient

* MM-11272 Added EmojiStore.GetMultipleByName

* MM-11272 Added emojis to PreparePostForClient

* MM-11272 Added unit tests for getting reaction counts

* MM-11272 Added unit tests for TestPreparePostForClient

* MM-11272 Added emojis from reactions to Post.Emojis

* MM-11272 Always update post.UpdateAt when reactions change to bust cache

* Fixed merge conflicts

* Moved post metadata-related code into its own file

* Update store mocks

* Fixed typo

* Add missing license headers

* Updated post metadata tests when custom emojis are disabled

* Fix unreliable unit tests

* Fix inconsistent casing in SQL statements

* Fix blank line

* Invalidate store cache after making changes

* Clear post cache synchronously with reactions

model/reaction.go

@@ -17,6 +17,8 @@ type Reaction struct {
 	CreateAt  int64  `json:"create_at"`
 }
 
+type ReactionCounts map[string]int
+
 func (o *Reaction) ToJson() string {
 	b, _ := json.Marshal(o)
 	return string(b)
@@ -74,3 +76,13 @@ func (o *Reaction) PreSave() {
 		o.CreateAt = GetMillis()
 	}
 }
+
+func CountReactions(reactions []*Reaction) ReactionCounts {
+	reactionCounts := ReactionCounts{}
+
+	for _, reaction := range reactions {
+		reactionCounts[reaction.EmojiName] += 1
+	}
+
+	return reactionCounts
+}