Supporting materialized views in Kusto

[ludwhe]

(Issue originally in ADS repo)

When querying an Azure Data Explorer connection, materialized views are not supported for autocompletion. When browsing it, materialized views are not shown. It would be nifty to have autocompletion for queries over materialized views, and to be able to list them from the Servers view.

I have implemented basic support in #2028, for now defaulting to displaying the views as table in the UI as displaying them as views requires an update of Kusto packages which causes regressions in connection management.