Extensibility: Context menu support in Object Explorer (#1883)

- Fixes #1867 context menu should be extensible
- Added context keys to support "when" conditions on the new extensions
- Fixes issue where actions like New Query, scripting show up even if these are not valid for the provider type or object type
- Fixed node expansion bug where rapid connect / expand / disconnect could break the app (fix in ObjectExplorerService.onNodeExpanded)
- Major change to how internal actions work. These cannot assume the context has non-serializable objects. Opened up some APIs to make this easier to handle.
- Fixed a number of existing bugs in internal actions.
  - Notably, DisconnectAction was adding a listener on each right-click on an active connection and never getting it disposed. This wasn't needed at all due to design changes.
  - Another bug fix is that the Manage action now correctly navigates to the DB dashboard for database-level connections. Before this it went to the server-level dashboard.

* Define API for context info

src/sql/services/bootstrap/bootstrapParams.ts

@@ -6,7 +6,7 @@
 import { DataService } from 'sql/parts/grid/services/dataService';
 import { IConnectionProfile } from 'sql/parts/connection/common/interfaces';
 import { IContextKeyService, IContextKey } from 'vs/platform/contextkey/common/contextkey';
-import { ConnectionContextkey } from 'sql/parts/connection/common/connectionContextKey';
+import { ConnectionContextKey } from 'sql/parts/connection/common/connectionContextKey';
 import { IBootstrapParams } from './bootstrapService';
 
 export interface IQueryComponentParams extends IBootstrapParams {
@@ -21,7 +21,7 @@ export interface IDefaultComponentParams extends IBootstrapParams {
 	connection: IConnectionProfile;
 	ownerUri: string;
 	scopedContextService: IContextKeyService;
-	connectionContextKey: ConnectionContextkey;
+	connectionContextKey: ConnectionContextKey;
 }
 
 export interface IDashboardComponentParams extends IDefaultComponentParams {