[G,S]etWindowLongPtrW are not available on 32-bit Windows, where [G,S]etWindowLongW should be used instead.
The initial revision of #14945 imported the win package for calling and other Win32 API functions, which exported
the correct API depending on the platform. However, the same logic wasn't implemented when we removed
the win package dependency in a later revision, resulting in panics on Windows 10 x86 (there's no 32-bit Windows 11).
In this PR, we update the ipn/desktop package to use either [G,S]etWindowLongPtrW or [G,S]etWindowLongW
depending on the platform.
Fixes#15684
Signed-off-by: Nick Khyl <nickk@tailscale.com>
This PR adds a new package, ipn/desktop, which provides a platform-agnostic
interface for enumerating desktop sessions and registering session callbacks.
Currently, it is implemented only for Windows.
Updates #14823
Signed-off-by: Nick Khyl <nickk@tailscale.com>
