(chocolatey#2112) Add msp support to Install helper

It's trivial to currently work with MSI installers with chocolately, as
we natively hook into msiexec's silent installation parameters to
complete the installation.

Support for msp files directly is a simple addition, as it uses the same
underlying msiexec installation method, with a slightly modified
parameter set.

src/chocolatey.resources/helpers/functions/Install-ChocolateyInstallPackage.ps1

@@ -249,7 +249,7 @@ Start-ChocolateyProcessAsAdmin
   }
 
   $installerTypeLower = $fileType.ToLower()
-  if ($installerTypeLower -ne 'msi' -and $installerTypeLower -ne 'exe' -and $installerTypeLower -ne 'msu') {
+  if ($installerTypeLower -notin 'msi', 'exe', 'msu', 'msp') {
     Write-Warning "FileType '$fileType' is unrecognized, using 'exe' instead."
     $fileType = 'exe'
   }
@@ -326,6 +326,19 @@ Pro / Business supports a single, ubiquitous install directory option.
 
   if ($fileType -like 'msi') {
     $msiArgs = "/i `"$fileFullPath`""
+    $msiArgs = if ($overrideArguments) {
+      Write-Host "Overriding package arguments with '$additonalInstallArgs' (replacing '$silentArgs')"
+      "$msiArgs $additionalInstallArgs"
+    }
+    else {
+      "$msiArgs $silentArgs $additionalInstallArgs"
+    }
+
+    $env:ChocolateyExitCode = Start-ChocolateyProcessAsAdmin "$msiArgs" "$($env:SystemRoot)\System32\msiexec.exe" -validExitCodes $validExitCodes -workingDirectory $workingDirectory
+  }
+
+  if ($fileType -like 'msp') {
+    $msiArgs = '/update "{0}"' -f $fileFullPath
     if ($overrideArguments) {
       Write-Host "Overriding package arguments with '$additionalInstallArgs' (replacing '$silentArgs')";
       $msiArgs = "$msiArgs $additionalInstallArgs";