Improve template system and panic recovery (#24461)

Partially for #24457

Major changes:

1. The old `signedUserNameStringPointerKey` is quite hacky, use
`ctx.Data[SignedUser]` instead
2. Move duplicate code from `Contexter` to `CommonTemplateContextData`
3. Remove incorrect copying&pasting code `ctx.Data["Err_Password"] =
true` in API handlers
4. Use one unique `RenderPanicErrorPage` for panic error page rendering
5. Move `stripSlashesMiddleware` to be the first middleware
6. Install global panic recovery handler, it works for both `install`
and `web`
7. Make `500.tmpl` only depend minimal template functions/variables,
avoid triggering new panics

Screenshot:

<details>

![image](https://user-images.githubusercontent.com/2114189/235444895-cecbabb8-e7dc-4360-a31c-b982d11946a7.png)

</details>

modules/web/route.go

@@ -25,12 +25,12 @@ func Bind[T any](_ T) any {
 }
 
 // SetForm set the form object
-func SetForm(data middleware.DataStore, obj interface{}) {
+func SetForm(data middleware.ContextDataStore, obj interface{}) {
 	data.GetData()["__form"] = obj
 }
 
 // GetForm returns the validate form information
-func GetForm(data middleware.DataStore) interface{} {
+func GetForm(data middleware.ContextDataStore) interface{} {
 	return data.GetData()["__form"]
 }