Refactor preferChocolatey system to handle other package managers easier (#3296)

* Easier to add more package managers changes

* style fixes

functions/private/Set-PackageManagerPreference.ps1

@@ -0,0 +1,45 @@
+function Set-PackageManagerPreference {
+    <#
+    .SYNOPSIS
+        Sets the currently selected package manager to global "ManagerPreference" in sync.
+        Also persists preference across Winutil restarts via preference.ini.
+
+        Reads from preference.ini if no argument sent.
+
+    .PARAMETER preferedPackageManager
+        The PackageManager that was selected.
+    #>
+    param(
+        [Parameter(Position=0, Mandatory=$false)]
+        [PackageManagers]$preferedPackageManager
+    )
+
+    $preferencePath = "$env:LOCALAPPDATA\winutil\preferences.ini"
+    $oldChocoPath = "$env:LOCALAPPDATA\winutil\preferChocolatey.ini"
+
+    #Try loading from file if no argument given.
+    if ($null -eq $preferedPackageManager) {
+        # Backwards compat for preferChocolatey.ini
+        if (Test-Path -Path $oldChocoPath) {
+            $preferedPackageManager = [PackageManagers]::Choco
+            Remove-Item -Path $oldChocoPath
+        }
+        else {
+            $potential = Get-Content -Path $preferencePath -TotalCount 1
+            if ($potential)
+                {$preferedPackageManager = [PackageManagers]$potential}
+        }
+    }
+
+    #If no preference argument, .ini file bad read, and $sync empty then default to winget.
+    if ($null -eq $preferedPackageManager -and $null -eq $sync["ManagerPreference"])
+        { $preferedPackageManager = [PackageManagers]::Winget }
+
+
+    $sync["ManagerPreference"] = [PackageManagers]::$preferedPackageManager
+    Write-Debug "Manager Preference changed to '$($sync["ManagerPreference"])'"
+
+
+    # Write preference to file to persist across restarts.
+    Out-File -FilePath $preferencePath -InputObject $sync["ManagerPreference"]
+}