On Windows arm64 we are going to need to ship two different GUI builds;
one for Win10 (GOARCH=386) and one for Win11 (GOARCH=amd64, tags +=
winui). Due to quirks in MSI packaging, they cannot both share the
same filename. This requires some fixes in places where we have
hardcoded "tailscale-ipn" as the GUI filename.
We also do some cleanup in clientupdate to ensure that autoupdates
will continue to work correctly with the temporary "-winui" package
variant.
Fixes#17480
Updates https://github.com/tailscale/corp/issues/29940
Signed-off-by: Aaron Klotz <aaron@tailscale.com>
