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

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

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

services/forms/runner.go

@@ -3,22 +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"
 
 // EditRunnerForm form for admin to create runner
 type EditRunnerForm struct {
+	middleware.FormDefaultValidator
 	Description string
 }
-
-// Validate validates form fields
-func (f *EditRunnerForm) Validate(req *http.Request, errs binding.Errors) binding.Errors {
-	ctx := context.GetValidateContext(req)
-	return middleware.Validate(ctx, errs, f)
-}