Fix uplevel SQL Server support and differentiate External and FileTable types in object explorer list (#567)

* Differentiate External and FileTable types in object explorer list
- Add (External) and (File Table) to the labels
- Pre-fetch these properties to avoid perf hit

Note on testing: These are both quite hard to initialize, so adding tests to the integration tests would require always having a server with Polybase enabled / FileTable enabled. Given this I feel it should be OK to use manual testing. Long term, we should have unit-level tests that cover the functionality or figure out how to have a perfect pre-configured server and a set of tests to run the breadth of this logic against it.

* Fix handling of vNext servers to default to latest known version
- Default uplevel / unknown versions to the latest version
- In the IsValidFor check also just see if the server version registers as "All" since this is the default for unknown servers. This is a backup handler, the 1st fix is the primary one

src/Microsoft.SqlTools.ServiceLayer/Localization/sr.it.resx

@@ -91,7 +91,7 @@
   <data name="EE_ExecutionInfo_QueryCancelledbyUser"><value>È stata annullata la query.</value></data>
   <data name="EE_BatchExecutionError_Halting"><value>Si è verificato un errore durante l'esecuzione del batch.</value></data>
   <data name="EE_BatchExecutionError_Ignoring"><value>Si è verificato un errore durante l'esecuzione del batch, ma l'errore è stato ignorato.</value></data>
-  <data name="EE_ExecutionInfo_InitializingLoop"><value>Avvio ciclo di esecuzione di {0} volte...</value></data>
+  <data name="EE_ExecutionInfo_InitializingLoop"><value>Beginning execution loop</value></data>
   <data name="EE_ExecutionError_CommandNotSupported"><value>Il comando {0} non è supportato.</value></data>
   <data name="EE_ExecutionError_VariableNotFound"><value>Impossibile trovare la variabile {0}.</value></data>
   <data name="BatchParserWrapperExecutionEngineError"><value>Errore di esecuzione di SQL: {0}</value></data>