fix(repo): unify DEFAULT_SHOW_FULL_NAME output in templates and dropdown (#36597)

The design of DefaultShowFullName has some problems, which make the UI
inconsistent, see the new comment in code

This PR does a clean up for various legacy problems, and clarify some
"user name display" behaviors.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/templates/helper.go

@@ -96,9 +96,6 @@ func NewFuncMap() template.FuncMap {
 		"AssetVersion": func() string {
 			return setting.AssetVersion
 		},
-		"DefaultShowFullName": func() bool {
-			return setting.UI.DefaultShowFullName
-		},
 		"ShowFooterTemplateLoadTime": func() bool {
 			return setting.Other.ShowFooterTemplateLoadTime
 		},

modules/templates/util_avatar.go

@@ -16,6 +16,7 @@ import (
 	user_model "code.gitea.io/gitea/models/user"
 	gitea_html "code.gitea.io/gitea/modules/htmlutil"
 	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/util"
 )
 
 type AvatarUtils struct {
@@ -29,13 +30,9 @@ func NewAvatarUtils(ctx context.Context) *AvatarUtils {
 // AvatarHTML creates the HTML for an avatar
 func AvatarHTML(src string, size int, class, name string) template.HTML {
 	sizeStr := strconv.Itoa(size)
-
-	if name == "" {
-		name = "avatar"
-	}
-
+	name = util.IfZero(name, "avatar")
 	// use empty alt, otherwise if the image fails to load, the width will follow the "alt" text's width
-	return template.HTML(`<img loading="lazy" alt class="` + class + `" src="` + src + `" title="` + html.EscapeString(name) + `" width="` + sizeStr + `" height="` + sizeStr + `"/>`)
+	return template.HTML(`<img loading="lazy" alt class="` + html.EscapeString(class) + `" src="` + html.EscapeString(src) + `" title="` + html.EscapeString(name) + `" width="` + sizeStr + `" height="` + sizeStr + `">`)
 }
 
 // Avatar renders user avatars. args: user, size (int), class (string)