[frontend, android] Move update_checker to frontend_common and add Android support

src/frontend_common/update_checker.h

@@ -0,0 +1,16 @@
+// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+// Copyright Citra Emulator Project / Azahar Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <optional>
+#include <string>
+
+namespace UpdateChecker {
+std::optional<std::string> GetResponse(std::string url, std::string path);
+std::optional<std::string> GetLatestRelease(bool include_prereleases);
+} // namespace UpdateChecker