Add support for 3D/CAD file formats preview (#34794)

Fix #34775 

---------

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

routers/web/repo/setting/lfs.go

@@ -267,8 +267,10 @@ func LFSFileGet(ctx *context.Context) {
 	buf = buf[:n]
 
 	st := typesniffer.DetectContentType(buf)
+	// FIXME: there is no IsPlainText set, but template uses it
 	ctx.Data["IsTextFile"] = st.IsText()
 	ctx.Data["FileSize"] = meta.Size
+	// FIXME: the last field is the URL-base64-encoded filename, it should not be "direct"
 	ctx.Data["RawFileLink"] = fmt.Sprintf("%s%s/%s.git/info/lfs/objects/%s/%s", setting.AppURL, url.PathEscape(ctx.Repo.Repository.OwnerName), url.PathEscape(ctx.Repo.Repository.Name), url.PathEscape(meta.Oid), "direct")
 	switch {
 	case st.IsRepresentableAsText():
@@ -309,8 +311,6 @@ func LFSFileGet(ctx *context.Context) {
 		}
 		ctx.Data["LineNums"] = gotemplate.HTML(output.String())
 
-	case st.IsPDF():
-		ctx.Data["IsPDFFile"] = true
 	case st.IsVideo():
 		ctx.Data["IsVideoFile"] = true
 	case st.IsAudio():