updating: split installer-related and github-related APIs, fix compilation error with latest VS

src/common/updating/installer.h

@@ -0,0 +1,19 @@
+#pragma once
+
+#include <string>
+#include <optional>
+#include <future>
+
+#include "notifications.h"
+#include "../VersionHelper.h"
+
+namespace updating
+{
+    std::wstring get_msi_package_path();
+    bool uninstall_msi_version(const std::wstring& package_path, const notifications::strings&);
+    bool offer_msi_uninstallation(const notifications::strings&);
+    std::optional<std::wstring> get_msi_package_installed_path();
+
+    std::optional<VersionHelper> get_installed_powertoys_version();
+    std::future<bool> uninstall_previous_msix_version_async();
+}