Start using template context function (#26254)

Before:

* `{{.locale.Tr ...}}`
* `{{$.locale.Tr ...}}`
* `{{$.root.locale.Tr ...}}`
* `{{template "sub" .}}`
* `{{template "sub" (dict "locale" $.locale)}}`
* `{{template "sub" (dict "root" $)}}`
* .....

With context function: only need to `{{ctx.Locale.Tr ...}}`

The "ctx" could be considered as a super-global variable for all
templates including sub-templates.


To avoid potential risks (any bug in the template context function
package), this PR only starts using "ctx" in "head.tmpl" and
"footer.tmpl" and it has a "DataRaceCheck". If there is anything wrong,
the code can be fixed or reverted easily.

routers/common/errpage.go

@@ -48,7 +48,7 @@ func RenderPanicErrorPage(w http.ResponseWriter, req *http.Request, err any) {
 		data["ErrorMsg"] = "PANIC: " + combinedErr
 	}
 
-	err = templates.HTMLRenderer().HTML(w, http.StatusInternalServerError, string(tplStatus500), data)
+	err = templates.HTMLRenderer().HTML(w, http.StatusInternalServerError, string(tplStatus500), data, nil)
 	if err != nil {
 		log.Error("Error occurs again when rendering error page: %v", err)
 		w.WriteHeader(http.StatusInternalServerError)