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>

modules/structs/admin_user.go

@@ -53,7 +53,7 @@ type EditUserOption struct {
 	// Whether the user must change password on next login
 	MustChangePassword *bool `json:"must_change_password"`
 	// The user's personal website URL
-	Website *string `json:"website" binding:"OmitEmpty;ValidUrl;MaxSize(255)"`
+	Website *string `json:"website" binding:"ValidUrl;MaxSize(255)"`
 	// The user's location or address
 	Location *string `json:"location" binding:"MaxSize(50)"`
 	// The user's personal description or bio