perf: apply perfpsrint linter (#33967) (#34632)

* perf: apply perfpsrint linter (#33967)

* perf: apply perfpsrint linter

* further simplifications

* improved TestParseHashtags coverage

* more simplifications

* simplify renderBlockHTML further

---------

Co-authored-by: Jesse Hallam <jesse@mattermost.com>

* Fixed a bad merge

---------

Co-authored-by: Catena cyber <35799796+catenacyber@users.noreply.github.com>
Co-authored-by: Jesse Hallam <jesse@mattermost.com>

server/public/model/utils.go

@@ -717,8 +717,8 @@ var (
 func ParseHashtags(text string) (string, string) {
 	words := strings.Fields(text)
 
-	hashtagString := ""
-	plainString := ""
+	var hashtagStringSb strings.Builder
+	var plainString strings.Builder
 	for _, word := range words {
 		// trim off surrounding punctuation
 		word = puncStart.ReplaceAllString(word, "")
@@ -728,11 +728,12 @@ func ParseHashtags(text string) (string, string) {
 		word = hashtagStart.ReplaceAllString(word, "#")
 
 		if validHashtag.MatchString(word) {
-			hashtagString += " " + word
+			hashtagStringSb.WriteString(" " + word)
 		} else {
-			plainString += " " + word
+			plainString.WriteString(" " + word)
 		}
 	}
+	hashtagString := hashtagStringSb.String()
 
 	if len(hashtagString) > 1000 {
 		hashtagString = hashtagString[:999]
@@ -744,7 +745,7 @@ func ParseHashtags(text string) (string, string) {
 		}
 	}
 
-	return strings.TrimSpace(hashtagString), strings.TrimSpace(plainString)
+	return strings.TrimSpace(hashtagString), strings.TrimSpace(plainString.String())
 }
 
 func ClearMentionTags(post string) string {