Refactor web route (#24080)

The old code is unnecessarily complex, and has many misuses.

Old code "wraps" a lot, wrap wrap wrap, it's difficult to understand
which kind of handler is used.

The new code uses a general approach, we do not need to write all kinds
of handlers into the "wrapper", do not need to wrap them again and
again.

New code, there are only 2 concepts:

1. HandlerProvider: `func (h any) (handlerProvider func (next)
http.Handler)`, it can be used as middleware
2. Use HandlerProvider to get the final HandlerFunc, and use it for
`r.Get()`


And we can decouple the route package from context package (see the
TODO).

# FAQ

## Is `reflect` safe?

Yes, all handlers are checked during startup, see the `preCheckHandler`
comment. If any handler is wrong, developers could know it in the first
time.

## Does `reflect` affect performance?

No. https://github.com/go-gitea/gitea/pull/24080#discussion_r1164825901

1. This reflect code only runs for each web handler call, handler is far
more slower: 10ms-50ms
2. The reflect is pretty fast (comparing to other code): 0.000265ms
3. XORM has more reflect operations already

routers/api/v1/api.go

@@ -634,8 +634,8 @@ func mustEnableAttachments(ctx *context.APIContext) {
 }
 
 // bind binding an obj to a func(ctx *context.APIContext)
-func bind[T any](obj T) http.HandlerFunc {
-	return web.Wrap(func(ctx *context.APIContext) {
+func bind[T any](_ T) any {
+	return func(ctx *context.APIContext) {
 		theObj := new(T) // create a new form obj for every request but not use obj directly
 		errs := binding.Bind(ctx.Req, theObj)
 		if len(errs) > 0 {
@@ -643,7 +643,7 @@ func bind[T any](obj T) http.HandlerFunc {
 			return
 		}
 		web.SetForm(ctx, theObj)
-	})
+	}
 }
 
 // The OAuth2 plugin is expected to be executed first, as it must ignore the user id stored