add platform function.

include/tray/platform/platform_enum.h

+#pragma once
+
+enum class Platform : int {
+  linux_, // linux is a marco
+  windows_,
+  macos_,
+  other_,
+};
+
+constexpr Platform get_platform_id() {
+
+#if defined(__linux__)
+  return Platform::linux_;
+#elif defined(TARGET_OS_MAC)
+  return Platform::macos_;
+#elif defined(_WIN32)
+  return Platform::windows_;
+#else
+  static_assert(false, "unknow platform");
+  return Platform::other_;
+#endif
+}
+#include <string_view>
+constexpr std::string_view get_platform_name() {
+  switch (get_platform_id()) {
+  case Platform::linux_:
+    return "Linux";
+  case Platform::macos_:
+    return "macOS";
+  case Platform::windows_:
+    return "Windows";
+  case Platform::other_:
+    return "Other";
+  }
+}