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.go

@@ -0,0 +1,28 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package sqlstore
+
+import (
+	"bytes"
+	"fmt"
+	"strconv"
+)
+
+// Converts a list of strings into a list of query parameters and a named parameter map that can
+// be used as part of a SQL query.
+func MapStringsToQueryParams(list []string, paramPrefix string) (string, map[string]interface{}) {
+	keys := bytes.Buffer{}
+	params := make(map[string]interface{})
+	for i, entry := range list {
+		if keys.Len() > 0 {
+			keys.WriteString(",")
+		}
+
+		key := paramPrefix + strconv.Itoa(i)
+		keys.WriteString(":" + key)
+		params[key] = entry
+	}
+
+	return fmt.Sprintf("(%v)", keys.String()), params
+}