Added Unified connection support (#3785)

* Added Unified connection support

* Use generic way to do expandNode.
Cleanup the ported code and removed unreference code. Added as needed later.
Resolved PR comments.

* Minor fixes and removed timer for all expanders for now. If any providers can't response, the tree node will spin and wait. We may improve later.

* Change handSessionClose to not thenable.
Added a node to OE to show error message instead of reject. So we could show partial expanded result if get any.
Resolve PR comments

* Minor fixes of PR comments

src/sql/workbench/api/common/sqlExtHostTypes.ts

@@ -288,6 +288,7 @@ export enum DataProviderType {
 	AgentServicesProvider = 'AgentServicesProvider',
 	CapabilitiesProvider = 'CapabilitiesProvider',
 	DacFxServicesProvider = 'DacFxServicesProvider',
+	ObjectExplorerNodeProvider = 'ObjectExplorerNodeProvider',
 }
 
 export enum DeclarativeDataType {
@@ -320,6 +321,17 @@ export enum AzureResource {
 	Sql = 1
 }
 
+export interface ServerInfoOption {
+	isBigDataCluster: boolean;
+	clusterEndpoints: ClusterEndpoint;
+}
+
+export interface ClusterEndpoint {
+	serviceName: string;
+	ipAddress: string;
+	port: number;
+}
+
 export class SqlThemeIcon {
 
 	static readonly Folder = new SqlThemeIcon('Folder');