Add datavirtualization extension (#21594)

* initial

* cleanup

* Add typings ref

* fix compile

* remove unused

* add missing

* another unused

* Use newer vscodetestcover

* newer dataprotocol

* format

* cleanup ignores

* fix out path

* fix entry point

* more cleanup

* Move into src folder

* Handle service client log messages

* remove unused

extensions/datavirtualization/src/fileSources.ts

@@ -0,0 +1,23 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the Source EULA. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import * as fs from 'fs';
+
+export interface IFile {
+	path: string;
+	isDirectory: boolean;
+}
+
+export interface IFileSource {
+
+	enumerateFiles(path: string): Promise<IFile[]>;
+	mkdir(dirName: string, remoteBasePath: string): Promise<void>;
+	createReadStream(path: string): fs.ReadStream;
+	readFile(path: string, maxBytes?: number): Promise<Buffer>;
+	readFileLines(path: string, maxLines: number): Promise<Buffer>;
+	writeFile(localFile: IFile, remoteDir: string): Promise<string>;
+	delete(path: string, recursive?: boolean): Promise<void>;
+	exists(path: string): Promise<boolean>;
+}