Create a unified dialog to ask user for offline name

Signed-off-by: Octol1ttle <l1ttleofficial@outlook.com>

launcher/ui/dialogs/ChooseOfflineNameDialog.h

@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: GPL-3.0-only
+/*
+ *  Prism Launcher - Minecraft Launcher
+ *  Copyright (C) 2025 Octol1ttle <l1ttleofficial@outlook.com>
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, version 3.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <QDialog>
+#include <QRegularExpressionValidator>
+
+QT_BEGIN_NAMESPACE
+namespace Ui {
+class ChooseOfflineNameDialog;
+}
+QT_END_NAMESPACE
+
+class ChooseOfflineNameDialog final : public QDialog {
+    Q_OBJECT
+
+   public:
+    explicit ChooseOfflineNameDialog(const QString& message, QWidget* parent = nullptr);
+    ~ChooseOfflineNameDialog() override;
+
+    QString getUsername() const;
+    void setUsername(const QString& username) const;
+
+   private:
+    void updateAcceptAllowed(const QString& username) const;
+
+   protected slots:
+    void on_usernameTextBox_textEdited(const QString& newText) const;
+    void on_allowInvalidUsernames_checkStateChanged(Qt::CheckState checkState) const;
+
+   private:
+    Ui::ChooseOfflineNameDialog* ui;
+    QRegularExpressionValidator* m_usernameValidator;
+};