Introduce platform services interface

src/platform_api/platform_services.h

@@ -0,0 +1,18 @@
+#pragma once
+
+#include <string>
+#include <string_view>
+
+namespace pp::platform {
+
+class PlatformServices {
+public:
+    virtual ~PlatformServices() = default;
+
+    [[nodiscard]] virtual std::string clipboard_text() = 0;
+    [[nodiscard]] virtual bool set_clipboard_text(std::string_view text) = 0;
+    virtual void set_cursor_visible(bool visible) = 0;
+    virtual void set_virtual_keyboard_visible(bool visible) = 0;
+};
+
+}