Mssql extension exposes OE getNode API for Sql-2019vNext extension (#3901)

* Mssql extension exposes OE getNode API for Sql-2019Vnext extension

* Resolved PR comments

extensions/mssql/src/api/mssqlapis.d.ts

@@ -0,0 +1,65 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the Source EULA. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+// This is the place for extensions to expose APIs.
+
+import * as sqlops from 'sqlops';
+import * as vscode from 'vscode';
+
+/**
+* The APIs provided by Mssql extension
+*
+* @export
+* @interface MssqlExtensionApi
+*/
+export interface MssqlExtensionApi {
+	/**
+	 * Gets the object explorer API that supports querying over the connections supported by this extension
+	 *
+	 * @returns {IMssqlObjectExplorerBrowser}
+	 * @memberof IMssqlExtensionApi
+	 */
+	getMssqlObjectExplorerBrowser(): MssqlObjectExplorerBrowser;
+}
+
+/**
+ * A browser supporting actions over the object explorer connections provided by this extension.
+ * Currently this is the
+ *
+ * @export
+ * @interface MssqlObjectExplorerBrowser
+ */
+export interface MssqlObjectExplorerBrowser {
+	/**
+	 * Gets the matching node given a context object, e.g. one from a right-click on a node in Object Explorer
+	 *
+	 * @param {sqlops.ObjectExplorerContext} objectExplorerContext
+	 * @returns {Promise<T>}
+	 */
+	getNode<T extends ITreeNode>(objectExplorerContext: sqlops.ObjectExplorerContext): Promise<T>;
+}
+
+/**
+ * A tree node in the object explorer tree
+ *
+ * @export
+ * @interface ITreeNode
+ */
+export interface ITreeNode {
+	getNodeInfo(): sqlops.NodeInfo;
+	getChildren(refreshChildren: boolean): ITreeNode[] | Promise<ITreeNode[]>;
+}
+
+/**
+ * A HDFS file node. This is a leaf node in the object explorer tree, and its contents
+ * can be queried
+ *
+ * @export
+ * @interface IFileNode
+ * @extends {ITreeNode}
+ */
+export interface IFileNode extends ITreeNode {
+	getFileContentsAsString(maxBytes?: number): Promise<string>;
+}