This PR is all about adding functionality that will enable the installer's
upgrade sequence to terminate processes belonging to the previous version,
and then subsequently restart instances belonging to the new version within
the session(s) corresponding to the processes that were killed.
There are multiple parts to this:
* We add support for the Restart Manager APIs, which allow us to query the
OS for a list of processes locking specific files;
* We add the RestartableProcess and RestartableProcesses types that query
additional information about the running processes that will allow us
to correctly restart them in the future. These types also provide the
ability to terminate the processes.
* We add the StartProcessInSession family of APIs that permit us to create
new processes within specific sessions. This is needed in order to
properly attach a new GUI process to the same RDP session and desktop that
its previously-terminated counterpart would have been running in.
* I tweaked the winutil token APIs again.
* A lot of this stuff is pretty hard to test without a very elaborate
harness, but I added a unit test for the most complicated part (though it
requires LocalSystem to run).
Updates https://github.com/tailscale/corp/issues/13998
Signed-off-by: Aaron Klotz <aaron@tailscale.com>
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