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_test.go

@@ -82,3 +82,38 @@ func TestReactionIsValid(t *testing.T) {
 		t.Fatal("create at should be invalid")
 	}
 }
+
+func TestCountReactions(t *testing.T) {
+	userId := NewId()
+	userId2 := NewId()
+
+	reactions := []*Reaction{
+		{
+			UserId:    userId,
+			EmojiName: "smile",
+		},
+		{
+			UserId:    userId,
+			EmojiName: "frowning",
+		},
+		{
+			UserId:    userId2,
+			EmojiName: "smile",
+		},
+		{
+			UserId:    userId2,
+			EmojiName: "neutral_face",
+		},
+	}
+
+	reactionCounts := CountReactions(reactions)
+	if len(reactionCounts) != 3 {
+		t.Fatal("should've received counts for 3 reactions")
+	} else if reactionCounts["smile"] != 2 {
+		t.Fatal("should've received 2 smile reactions")
+	} else if reactionCounts["frowning"] != 1 {
+		t.Fatal("should've received 1 frowning reaction")
+	} else if reactionCounts["neutral_face"] != 1 {
+		t.Fatal("should've received 2 neutral_face reaction")
+	}
+}