qt/applets: Provide Qt frontend implementation of software keyboard

Implements all of the features of the keyboard, including length, default text, character validation, and UTF-16 character support.

src/yuzu/applets/software_keyboard.h

@@ -0,0 +1,62 @@
+// Copyright 2018 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+#include <QDialog>
+#include <QValidator>
+#include "common/assert.h"
+#include "core/frontend/applets/software_keyboard.h"
+
+class QDialogButtonBox;
+class QLabel;
+class QLineEdit;
+class QVBoxLayout;
+class QtSoftwareKeyboard;
+
+class QtSoftwareKeyboardValidator final : public QValidator {
+public:
+    explicit QtSoftwareKeyboardValidator(Frontend::SoftwareKeyboardApplet::Parameters parameters);
+    State validate(QString&, int&) const override;
+
+private:
+    Frontend::SoftwareKeyboardApplet::Parameters parameters;
+};
+
+class QtSoftwareKeyboardDialog final : public QDialog {
+    Q_OBJECT
+
+public:
+    QtSoftwareKeyboardDialog(QWidget* parent,
+                             Frontend::SoftwareKeyboardApplet::Parameters parameters);
+    void Submit();
+    void Reject();
+
+private:
+    bool ok = false;
+    std::u16string text;
+
+    QDialogButtonBox* buttons;
+    QLabel* header_label;
+    QLabel* sub_label;
+    QLabel* guide_label;
+    QLineEdit* line_edit;
+    QVBoxLayout* layout;
+
+    Frontend::SoftwareKeyboardApplet::Parameters parameters;
+
+    friend class QtSoftwareKeyboard;
+};
+
+class QtSoftwareKeyboard final : public QObject, public Frontend::SoftwareKeyboardApplet {
+public:
+    explicit QtSoftwareKeyboard(QWidget& parent);
+    bool GetText(Parameters parameters, std::u16string& text) override;
+
+    ~QtSoftwareKeyboard() {
+        UNREACHABLE();
+    }
+
+private:
+    QWidget& parent;
+};