Port most notebook model code over to be behind a service (#3068)

- Defines a new NotebookService in Azure Data Studio which will be used to interact with notebooks. Since notebooks can require per-file instantiation the provider is just used to create & track managers for a given URI.
- Inject this into notebook.component.ts and pass required parameters that'll be used to properly initialize a manger into the method. Actual initialization not done yet.
- Port over & recompile notebook model code
- Define most required APIs in sqlops.proposed.d.ts. In the future, these will be used by extensions to contribute their own providers.

src/sql/parts/notebook/notebookUtils.ts

@@ -0,0 +1,38 @@
+/*---------------------------------------------------------------------------------------------
+ *  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 { nb } from 'sqlops';
+import * as os from 'os';
+import * as pfs from 'vs/base/node/pfs';
+import { localize } from 'vs/nls';
+import { IOutputChannel } from 'vs/workbench/parts/output/common/output';
+
+
+/**
+ * Test whether an output is from a stream.
+ */
+export function isStream(output: nb.ICellOutput): output is nb.IStreamResult {
+	return output.output_type === 'stream';
+}
+
+export function getErrorMessage(error: Error | string): string {
+	return (error instanceof Error) ? error.message : error;
+}
+
+export function getUserHome(): string {
+	return process.env.HOME || process.env.USERPROFILE;
+}
+
+export async function mkDir(dirPath: string, outputChannel?: IOutputChannel): Promise<void> {
+	let exists = await pfs.dirExists(dirPath);
+	if (!exists) {
+		if (outputChannel) {
+			outputChannel.append(localize('mkdirOutputMsg', '... Creating {0}', dirPath) + os.EOL);
+		}
+		await pfs.mkdirp(dirPath);
+	}
+}