refactor: http request binding (#38971)

Better than before, still not good enough (more work can be done in the
future)

And add the missing error handling in the PrivateContext "bind"
middleware.

By the way, picked some "TrimSpace" changes from "fix: trim whitespace
from SMTP address and port - #38934" (fix #38926)

modules/structs/form.go

@@ -4,20 +4,14 @@
 package structs
 
 import (
-	"net/http"
-
-	"gitea.dev/modules/reqctx"
 	"gitea.dev/modules/translation/i18n"
 
-	"gitea.com/go-chi/binding"
+	"gitea.com/go-chi/binding" //nolint:depguard // avoid cycle import
 )
 
 // ValidateContext is a special context for form validation middleware
 type ValidateContext struct {
 	Locale i18n.LocaleTranslation
-	Data   reqctx.ContextData
-	Req    *http.Request
-	Resp   http.ResponseWriter
 }
 
 type FormDefaultValidator struct{}