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/web/middleware/binding_test.go

@@ -4,13 +4,11 @@
 package middleware
 
 import (
-	"net/http"
-	"net/http/httptest"
 	"testing"
 
 	"gitea.dev/modules/translation"
+	"gitea.dev/modules/validation"
 
-	"gitea.com/go-chi/binding"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -22,7 +20,7 @@ type testRangeForm struct {
 func TestBuildValidationErrorForUser(t *testing.T) {
 	// an out-of-range value must reach its own message instead of the panicking "default" branch
 	form := &testRangeForm{Hours: 2000}
-	errs := binding.Validate(httptest.NewRequest(http.MethodPost, "/", nil), form)
+	errs := validation.Binder().Validate(t.Context(), form)
 	errorMessage, errorFieldName, fieldNames := BuildValidationErrorForUser(form, translation.MockLocale{}, errs)
 	assert.Equal(t, "form.range_error:form.Hours,0,1000", errorMessage)
 	assert.Equal(t, "Hours", errorFieldName)