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

extensions/mssql/src/objectExplorerNodeProvider/treeNodes.ts

@@ -0,0 +1,78 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the Source EULA. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+'use strict';
+
+import * as sqlops from 'sqlops';
+import * as vscode from 'vscode';
+import { ITreeNode } from './types';
+
+type TreeNodePredicate = (node: TreeNode) => boolean;
+
+export abstract class TreeNode implements ITreeNode {
+	private _parent: TreeNode = undefined;
+
+	public get parent(): TreeNode {
+		return this._parent;
+	}
+
+	public set parent(node: TreeNode) {
+		this._parent = node;
+	}
+
+	public generateNodePath(): string {
+		let path = undefined;
+		if (this.parent) {
+			path = this.parent.generateNodePath();
+		}
+		path = path ? `${path}/${this.nodePathValue}` : this.nodePathValue;
+		return path;
+	}
+
+	public findNodeByPath(path: string, expandIfNeeded: boolean = false): Promise<TreeNode> {
+		let condition: TreeNodePredicate = (node: TreeNode) => node.getNodeInfo().nodePath === path || node.getNodeInfo().nodePath.startsWith(path);
+		let filter: TreeNodePredicate = (node: TreeNode) => path.startsWith(node.getNodeInfo().nodePath);
+		return TreeNode.findNode(this, condition, filter, true);
+	}
+
+	public static async findNode(node: TreeNode, condition: TreeNodePredicate, filter: TreeNodePredicate, expandIfNeeded: boolean): Promise<TreeNode> {
+		if (!node) {
+			return undefined;
+		}
+
+		if (condition(node)) {
+			return node;
+		}
+
+		let nodeInfo = node.getNodeInfo();
+		if (nodeInfo.isLeaf) {
+			return undefined;
+		}
+
+		// TODO #3813 support filtering by already expanded / not yet expanded
+		let children = await node.getChildren(false);
+		if (children) {
+			for (let child of children) {
+				if (filter && filter(child)) {
+					let childNode =  await this.findNode(child, condition, filter, expandIfNeeded);
+					if (childNode) {
+						return childNode;
+					}
+				}
+			}
+		}
+		return undefined;
+	}
+
+	/**
+	 * The value to use for this node in the node path
+	 */
+	public abstract get nodePathValue(): string;
+
+	abstract getChildren(refreshChildren: boolean): TreeNode[] | Promise<TreeNode[]>;
+	abstract getTreeItem(): vscode.TreeItem | Promise<vscode.TreeItem>;
+
+	abstract getNodeInfo(): sqlops.NodeInfo;
+}