Move internal packages to an internal folder

For reference: https://go.dev/doc/go1.4#internalpackages

ui/form/user.go

@@ -1,73 +0,0 @@
-// SPDX-FileCopyrightText: Copyright The Miniflux Authors. All rights reserved.
-// SPDX-License-Identifier: Apache-2.0
-
-package form // import "miniflux.app/v2/ui/form"
-
-import (
-	"net/http"
-
-	"miniflux.app/v2/errors"
-	"miniflux.app/v2/model"
-)
-
-// UserForm represents the user form.
-type UserForm struct {
-	Username     string
-	Password     string
-	Confirmation string
-	IsAdmin      bool
-}
-
-// ValidateCreation validates user creation.
-func (u UserForm) ValidateCreation() error {
-	if u.Username == "" || u.Password == "" || u.Confirmation == "" {
-		return errors.NewLocalizedError("error.fields_mandatory")
-	}
-
-	if u.Password != u.Confirmation {
-		return errors.NewLocalizedError("error.different_passwords")
-	}
-
-	return nil
-}
-
-// ValidateModification validates user modification.
-func (u UserForm) ValidateModification() error {
-	if u.Username == "" {
-		return errors.NewLocalizedError("error.user_mandatory_fields")
-	}
-
-	if u.Password != "" {
-		if u.Password != u.Confirmation {
-			return errors.NewLocalizedError("error.different_passwords")
-		}
-
-		if len(u.Password) < 6 {
-			return errors.NewLocalizedError("error.password_min_length")
-		}
-	}
-
-	return nil
-}
-
-// Merge updates the fields of the given user.
-func (u UserForm) Merge(user *model.User) *model.User {
-	user.Username = u.Username
-	user.IsAdmin = u.IsAdmin
-
-	if u.Password != "" {
-		user.Password = u.Password
-	}
-
-	return user
-}
-
-// NewUserForm returns a new UserForm.
-func NewUserForm(r *http.Request) *UserForm {
-	return &UserForm{
-		Username:     r.FormValue("username"),
-		Password:     r.FormValue("password"),
-		Confirmation: r.FormValue("confirmation"),
-		IsAdmin:      r.FormValue("is_admin") == "1",
-	}
-}