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

store/sqlstore/utils_test.go

@@ -0,0 +1,32 @@
+package sqlstore
+
+import (
+	"testing"
+)
+
+func TestMapStringsToQueryParams(t *testing.T) {
+	t.Run("one item", func(t *testing.T) {
+		input := []string{"apple"}
+
+		keys, params := MapStringsToQueryParams(input, "Fruit")
+
+		if len(params) != 1 || params["Fruit0"] != "apple" {
+			t.Fatal("returned incorrect params", params)
+		} else if keys != "(:Fruit0)" {
+			t.Fatal("returned incorrect query", keys)
+		}
+	})
+
+	t.Run("multiple items", func(t *testing.T) {
+		input := []string{"carrot", "tomato", "potato"}
+
+		keys, params := MapStringsToQueryParams(input, "Vegetable")
+
+		if len(params) != 3 || params["Vegetable0"] != "carrot" ||
+			params["Vegetable1"] != "tomato" || params["Vegetable2"] != "potato" {
+			t.Fatal("returned incorrect params", params)
+		} else if keys != "(:Vegetable0,:Vegetable1,:Vegetable2)" {
+			t.Fatal("returned incorrect query", keys)
+		}
+	})
+}