Add Image Diff for SVG files (#14867)

* Added type sniffer.

* Switched content detection from base to typesniffer.

* Added GuessContentType to Blob.

* Moved image info logic to client.
Added support for SVG images in diff.

* Restore old blocked svg behaviour.

* Added missing image formats.

* Execute image diff only when container is visible.

* add margin to spinner

* improve BIN tag on image diffs

* Default to render view.

* Show image diff on incomplete diff.

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Lauris BH <lauris@nix.lv>

routers/user/setting/profile.go

@@ -19,6 +19,7 @@ import (
 	"code.gitea.io/gitea/modules/context"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/typesniffer"
 	"code.gitea.io/gitea/modules/util"
 	"code.gitea.io/gitea/modules/web"
 	"code.gitea.io/gitea/modules/web/middleware"
@@ -159,7 +160,9 @@ func UpdateAvatarSetting(ctx *context.Context, form *forms.AvatarForm, ctxUser *
 		if err != nil {
 			return fmt.Errorf("ioutil.ReadAll: %v", err)
 		}
-		if !base.IsImageFile(data) {
+
+		st := typesniffer.DetectContentType(data)
+		if !(st.IsImage() && !st.IsSvgImage()) {
 			return errors.New(ctx.Tr("settings.uploaded_avatar_not_a_image"))
 		}
 		if err = ctxUser.UploadAvatar(data); err != nil {