refactor: clean up form binding & validation (#38873)

Clarify the "validation" and "error display" logic.

All the copied&pasted `Validate` functions are removed.

services/forms/package_form.go

@@ -3,16 +3,10 @@
 
 package forms
 
-import (
-	"net/http"
-
-	"gitea.dev/modules/web/middleware"
-	"gitea.dev/services/context"
-
-	"gitea.com/go-chi/binding"
-)
+import "gitea.dev/modules/web/middleware"
 
 type PackageCleanupRuleForm struct {
+	middleware.FormDefaultValidator
 	ID            int64
 	Enabled       bool
 	Type          string `binding:"Required;In(alpine,arch,cargo,chef,composer,conan,conda,container,cran,debian,generic,go,helm,maven,npm,nuget,pub,pypi,rpm,rubygems,swift,terraform,vagrant)"`
@@ -23,8 +17,3 @@ type PackageCleanupRuleForm struct {
 	MatchFullName bool
 	Action        string `binding:"Required;In(save,remove)"`
 }
-
-func (f *PackageCleanupRuleForm) Validate(req *http.Request, errs binding.Errors) binding.Errors {
-	ctx := context.GetValidateContext(req)
-	return middleware.Validate(ctx, errs, f)
-}