refactor: move go-chi/binding into Gitea (#39528)

The `gitea.com/go-chi/binding` package only exists for Gitea, so it
moves into `modules/web/binding` to fix its bugs directly. Split out of
https://github.com/go-gitea/gitea/pull/39504.

- GET and HEAD always bind the query
- JSON `null` slice elements and nested `TrimSpace` fields bind
correctly
- Integer fields reject out-of-range values instead of wrapping
- An empty JSON body binds nothing and an unknown binding rule is an
error

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

go.mod

@@ -6,7 +6,6 @@ toolchain go1.27.1
 
 require (
 	connectrpc.com/connect v1.21.0
-	gitea.com/go-chi/binding v0.0.0-20260819122636-082915a69981
 	gitea.com/go-chi/cache v0.2.1
 	gitea.com/go-chi/captcha v0.0.0-20240315150714-fb487f629098
 	gitea.com/go-chi/session v0.0.0-20260708011333-ebced8a7a2d6