WIP Enhance Start-EditorServices.ps1 for better logging and fix bugs (#1198)

* Initial stab at logging PSES startup script

* Try different approach to find ports in use

* Revert back to Test-PortAvailability due to missing .NET Core features

Modify Test-PortAvailability to check each address (ipv4 and ipv6) in
AddressList for localhost.

* Add blank line between func defs

* Revert bool condition check, $true on RHS

* Add support for Diagnostic log level

Set Start-EditorServices to log only for Diagnostic log level.

Add string enum support for log level so in UserSettings you get a list.

Author: rkeithhill

package.json

@@ -502,8 +502,15 @@
         },
         "powershell.developer.editorServicesLogLevel": {
           "type": "string",
+          "enum": [
+            "Diagnostic",
+            "Verbose",
+            "Normal",
+            "Warning",
+            "Error"
+          ],
           "default": "Normal",
-          "description": "Sets the logging verbosity level for the PowerShell Editor Services host executable.  Valid values are 'Verbose', 'Normal', 'Warning', and 'Error'"
+          "description": "Sets the logging verbosity level for the PowerShell Editor Services host executable.  Valid values are 'Diagnostic', 'Verbose', 'Normal', 'Warning', and 'Error'"
         },
         "powershell.developer.editorServicesWaitForDebugger": {
           "type": "boolean",