I realized that a lot of the problems that we're seeing around migration and
LocalBackend state can be avoided if we drive Windows pref migration entirely
from within tailscaled. By doing it this way, tailscaled can automatically
perform the migration as soon as the connection with the client frontend is
established.
Since tailscaled is already running as LocalSystem, it already has access to
the user's local AppData directory. The profile manager already knows which
user is connected, so we simply need to resolve the user's prefs file and read
it from there.
Of course, to properly migrate this information we need to also check system
policies. I moved a bunch of policy resolution code out of the GUI and into
a new package in util/winutil/policy.
Updates #7626
Signed-off-by: Aaron Klotz <aaron@tailscale.com>
90fd04cbde