Improve template helper (#24417)

It seems that we really need the "context function" soon. So we should
clean up the helper functions first.

Major changes:

* Improve StringUtils and add JsonUtils
* Remove one-time-use helper functions like CompareLink
* Move other code (no change) to util_avatar/util_render/util_misc (no
need to propose changes for them)

I have tested the changed templates:


![image](https://user-images.githubusercontent.com/2114189/235283862-608dbf6b-2da3-4d06-8157-b523ca93edb4.png)


![image](https://user-images.githubusercontent.com/2114189/235283888-1dfc0471-e622-4d64-9d76-7859819580d3.png)


![image](https://user-images.githubusercontent.com/2114189/235283903-d559f14d-4abb-4a50-915f-2b9cbc381a7a.png)


![image](https://user-images.githubusercontent.com/2114189/235283955-b7b5adea-aca3-4758-b38a-3aae3f7c6048.png)

---------

Co-authored-by: Giteabot <teabot@gitea.io>

modules/templates/util_avatar.go

@@ -0,0 +1,84 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package templates
+
+import (
+	"context"
+	"fmt"
+	"html"
+	"html/template"
+
+	activities_model "code.gitea.io/gitea/models/activities"
+	"code.gitea.io/gitea/models/avatars"
+	"code.gitea.io/gitea/models/organization"
+	repo_model "code.gitea.io/gitea/models/repo"
+	user_model "code.gitea.io/gitea/models/user"
+	gitea_html "code.gitea.io/gitea/modules/html"
+	"code.gitea.io/gitea/modules/setting"
+)
+
+// AvatarHTML creates the HTML for an avatar
+func AvatarHTML(src string, size int, class, name string) template.HTML {
+	sizeStr := fmt.Sprintf(`%d`, size)
+
+	if name == "" {
+		name = "avatar"
+	}
+
+	return template.HTML(`<img class="` + class + `" src="` + src + `" title="` + html.EscapeString(name) + `" width="` + sizeStr + `" height="` + sizeStr + `"/>`)
+}
+
+// Avatar renders user avatars. args: user, size (int), class (string)
+func Avatar(ctx context.Context, item interface{}, others ...interface{}) template.HTML {
+	size, class := gitea_html.ParseSizeAndClass(avatars.DefaultAvatarPixelSize, avatars.DefaultAvatarClass, others...)
+
+	switch t := item.(type) {
+	case *user_model.User:
+		src := t.AvatarLinkWithSize(ctx, size*setting.Avatar.RenderedSizeFactor)
+		if src != "" {
+			return AvatarHTML(src, size, class, t.DisplayName())
+		}
+	case *repo_model.Collaborator:
+		src := t.AvatarLinkWithSize(ctx, size*setting.Avatar.RenderedSizeFactor)
+		if src != "" {
+			return AvatarHTML(src, size, class, t.DisplayName())
+		}
+	case *organization.Organization:
+		src := t.AsUser().AvatarLinkWithSize(ctx, size*setting.Avatar.RenderedSizeFactor)
+		if src != "" {
+			return AvatarHTML(src, size, class, t.AsUser().DisplayName())
+		}
+	}
+
+	return template.HTML("")
+}
+
+// AvatarByAction renders user avatars from action. args: action, size (int), class (string)
+func AvatarByAction(ctx context.Context, action *activities_model.Action, others ...interface{}) template.HTML {
+	action.LoadActUser(ctx)
+	return Avatar(ctx, action.ActUser, others...)
+}
+
+// RepoAvatar renders repo avatars. args: repo, size(int), class (string)
+func RepoAvatar(repo *repo_model.Repository, others ...interface{}) template.HTML {
+	size, class := gitea_html.ParseSizeAndClass(avatars.DefaultAvatarPixelSize, avatars.DefaultAvatarClass, others...)
+
+	src := repo.RelAvatarLink()
+	if src != "" {
+		return AvatarHTML(src, size, class, repo.FullName())
+	}
+	return template.HTML("")
+}
+
+// AvatarByEmail renders avatars by email address. args: email, name, size (int), class (string)
+func AvatarByEmail(ctx context.Context, email, name string, others ...interface{}) template.HTML {
+	size, class := gitea_html.ParseSizeAndClass(avatars.DefaultAvatarPixelSize, avatars.DefaultAvatarClass, others...)
+	src := avatars.GenerateEmailAvatarFastLink(ctx, email, size*setting.Avatar.RenderedSizeFactor)
+
+	if src != "" {
+		return AvatarHTML(src, size, class, name)
+	}
+
+	return template.HTML("")
+}