Qt: Add config and implementation for basic controller input

src/duckstation-qt/qtutils.h

@@ -1,5 +1,7 @@
 #pragma once
+#include <QtCore/QString>
 #include <initializer_list>
+#include <optional>
 
 class QTableView;
 
@@ -9,4 +11,10 @@ namespace QtUtils {
 /// remaining space.
 void ResizeColumnsForTableView(QTableView* view, const std::initializer_list<int>& widths);
 
+/// Returns a string identifier for a Qt key ID.
+QString GetKeyIdentifier(int key);
+
+/// Returns the integer Qt key ID for an identifier.
+std::optional<int> GetKeyIdForIdentifier(const QString& key_identifier);
+
 } // namespace QtUtils