(GH-902) Fix: User changed to SYSTEM during env update

Previously, running RefreshEnv / Update-SessionEnvironment would change
current user to SYSTEM. This is due to Machine environment variables
noting user as SYSTEM. To stop this, set the original username as a
variable and reset the Username environment variable after the refresh.

Do the same for Processor_Architecture.

src/chocolatey.resources/helpers/functions/Update-SessionEnvironment.ps1

@@ -59,6 +59,8 @@ None
     Write-Verbose "Refreshing environment variables from the registry."
   }
 
+  $userName = $env:USERNAME
+  $architecture = $env:PROCESSOR_ARCHITECTURE
   $psModulePath = $env:PSModulePath
 
   #ordering is important here, $user comes after so we can override $machine
@@ -82,6 +84,10 @@ None
   # PSModulePath is almost always updated by process, so we want to preserve it.
   $env:PSModulePath = $psModulePath
 
+  # reset user and architecture
+  if ($userName) { $env:USERNAME = $userName; }
+  if ($architecture) { $env:PROCESSOR_ARCHITECTURE = $architecture; }
+
   if ($refreshEnv) {
     Write-Output "Finished"
   }

src/chocolatey.resources/redirects/RefreshEnv.cmd

@@ -49,8 +49,16 @@ goto main
     del /f /q "%TEMP%\_envset.tmp" 2>nul
     del /f /q "%TEMP%\_envget.tmp" 2>nul
 
+    :: capture user / architecture
+    SET "OriginalUserName=%USERNAME%"
+    SET "OriginalArchitecture=%PROCESSOR_ARCHITECTURE%"
+
     :: Set these variables
     call "%TEMP%\_env.cmd"
 
+    :: reset user / architecture
+    SET "USERNAME=%OriginalUserName%"
+    SET "PROCESSOR_ARCHITECTURE=%OriginalArchitecture%"
+
     echo | set /p dummy="Finished."
     echo .