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/cancelableStream.ts

@@ -0,0 +1,25 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the Source EULA. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import { Transform } from 'stream';
+import * as vscode from 'vscode';
+import * as nls from 'vscode-nls';
+
+const localize = nls.loadMessageBundle();
+
+export class CancelableStream extends Transform {
+	constructor(private cancelationToken: vscode.CancellationTokenSource) {
+		super();
+	}
+
+	public _transform(chunk: any, encoding: string, callback: Function): void {
+		if (this.cancelationToken && this.cancelationToken.token.isCancellationRequested) {
+			callback(new Error(localize('streamCanceled', 'Stream operation canceled by the user')));
+		} else {
+			this.push(chunk);
+			callback();
+		}
+	}
+}