Data Explorer Sourcing (#4033)

* added initial data explorer viewlet

* added dataexplorer contribution point

* removed test view

* remove unused imports

* inital data source, needs work

* add shim for ext host

* formatting

* making the necessary changes to use OE for tree view; need to look at TreeUpdateUtils.connectAndCreateOeSession

* formatting

* shimming oe more

* update to add correct context

* working cross provider; need to fix connection

* connection works but it adds the connection to the oe for some reason

* formatting

* add custom connection dialog code path

* hashing between trees

* added flag and tests

* add id maps to handle multiple nodepaths

* add necessary car edit parts

* keep current behavior in prodc

* fix tests

* address comments

* update comments to be more informative

* finish merge

* update comments

* fix whitespace

src/sql/workbench/api/node/sqlExtHost.api.impl.ts

@@ -547,6 +547,7 @@ export function createApiFactory(
 				nb: nb,
 				AzureResource: sqlExtHostTypes.AzureResource,
 				extensions: extensions,
+				TreeItem: sqlExtHostTypes.TreeItem,
 			};
 		}
 	};