Fix deferred telemetry pipe attach for RDP sessions

[tyrielv]

At startup, the deferred telemetry attacher only checked the physical console session via WTSGetActiveConsoleSessionId. On Cloud PCs and RDP-only machines, the console session has no logged-in user — the real user is in an RDP session. This meant the startup attach always failed, the retry timer could never succeed (SYSTEM has no git global config), and no SessionLogon event fires for already-connected users.

Fix

Enumerate all interactive sessions (Active/Connected, session > 0) via WTSEnumerateSessions and try each until the pipe attaches.

Changes

• CurrentUser.cs: Add public GetInteractiveSessionIds that filters WTSEnumerateSessions to Active/Connected sessions with ID > 0
• GVFSService.Windows.cs: Replace single console session check with TryAttachTelemetryPipeForAnySessions that iterates all interactive sessions; move telemetry attacher setup before PendingUpgradeHandler so deferred-upgrade events are buffered
• Log levels: Downgrade token-query failure from Error to Warning (expected on Cloud PCs where the console session has no user)
• AOT warnings: Use generic Marshal.SizeOf<T>() and Marshal.PtrToStructure<T>() instead of typeof() overloads

Testing

• All 818 unit tests pass
• Verified locally on Cloud PC (RDP-only): telemetry pipe attaches via RDP session after console session fails
• VFS.Service.PendingUpgradeHandler_Deferred and VFS.Service.PendingUpgradeHandler_Complete confirmed in App Insights