Improve efficiency of `consoleusers.CurrentUids` and `consoleusers.ExplorerProcess`

[RebeccaMahany]

Right now, on Windows, the new consoleusers.CurrentUids implementation added in #2422 is incorrectly identifying additional users that we should start desktop processes for. This means that the desktop runner is, every five seconds, trying to start a desktop process for these users, which means it calls consoleusers.ExplorerProcess and enumerates every single process. This is very noisy in the logs, and we suspect there's a performance impact. (This issue will, though, be invisible to the end user otherwise.)

For the next release:

• Figure out how to correctly filter out users that we shouldn't create login sessions for (or, at the very least, hardcode known exceptions into consoleusers.CurrentUids): Exclude some sessions from list of current UIDs #2465

Over the next two releases:

• Complete Desktop runner should respond to changes in DesktopUpdateInterval #2462, so that we can increase the interval on the cloud side
• Figure out an alternative to consoleusers.ExplorerProcess that doesn't require enumerating every single process
• Evaluate performance impact of current consoleusers.CurrentUids implementation on macOS and Linux

In the long term:

• Investigate subscribing to logon events so that we don't have to run this check quite so frequently (or maybe we can phase it out altogether)

[RebeccaMahany]

Quick note that I benchmarked options for ExplorerProcess using query process, Get-Process, tasklist -- and all of them were 1-2x orders of magnitude slower.