Support Notebook integration testing by adding APIs & fixing others (#3848)

- Added `runCell` API. Updated runCell button to listen to events on the model so it'll reflect run cell when called from other sources
- Plumbed through kernelspec info to the extension side so when changed, it's updated
- Fixed bug in ConnectionProfile where it didn't copy from options but instead overrode with empty wrapper functions

Here's the rough test code (it's in the sql-vnext extension and will be out in a separate PR)
```ts

    it('Should connect to local notebook server with result 2', async function() {
        this.timeout(60000);
        let pythonNotebook = Object.assign({}, expectedNotebookContent, { metadata: { kernelspec: { name: "python3", display_name: "Python 3" }}});
        let uri = writeNotebookToFile(pythonNotebook);
        await ensureJupyterInstalled();

        let notebook = await sqlops.nb.showNotebookDocument(uri);
        should(notebook.document.cells).have.length(1);
        let ran = await notebook.runCell(notebook.document.cells[0]);
        should(ran).be.true('Notebook runCell failed');
        let cellOutputs = notebook.document.cells[0].contents.outputs;
        should(cellOutputs).have.length(1);
        let result = (<sqlops.nb.IExecuteResult>cellOutputs[0]).data['text/plain'];
        should(result).equal('2');

        try {
            // TODO support closing the editor. Right now this prompts and there's no override for this. Need to fix in core
            // Close the editor using the recommended vscode API
            //await vscode.commands.executeCommand('workbench.action.closeActiveEditor');
        }
        catch (e) {}
    });

    it('Should connect to remote spark server with result 2', async function() {
        this.timeout(240000);
        let uri = writeNotebookToFile(expectedNotebookContent);
        await ensureJupyterInstalled();

        // Given a connection to a server exists
        let connectionId = await connectToSparkIntegrationServer();

        // When I open a Spark notebook and run the cell
        let notebook = await sqlops.nb.showNotebookDocument(uri, {
            connectionId: connectionId
        });
        should(notebook.document.cells).have.length(1);
        let ran = await notebook.runCell(notebook.document.cells[0]);
        should(ran).be.true('Notebook runCell failed');

        // Then I expect to get the output result of 1+1, executed remotely against the Spark endpoint
        let cellOutputs = notebook.document.cells[0].contents.outputs;
        should(cellOutputs).have.length(4);
        let sparkResult = (<sqlops.nb.IStreamResult>cellOutputs[3]).text;
        should(sparkResult).equal('2');

        try {
            // TODO support closing the editor. Right now this prompts and there's no override for this. Need to fix in core
            // Close the editor using the recommended vscode API
            //await vscode.commands.executeCommand('workbench.action.closeActiveEditor');
        }
        catch (e) {}
    });
});
```

src/sql/parts/notebook/models/modelInterfaces.ts

@@ -127,6 +127,8 @@ export interface IClientSession extends IDisposable {
 	 */
 	readonly kernelDisplayName: string;
 
+	readonly cachedKernelSpec: nb.IKernelSpec;
+
 	/**
 	 * Initializes the ClientSession, by starting the server and
 	 * connecting to the SessionManager.
@@ -200,7 +202,13 @@ export interface IClientSession extends IDisposable {
 	/**
 	 * Updates the connection
 	 */
-	updateConnection(connection: IConnectionProfile): void;
+	updateConnection(connection: IConnectionProfile): Promise<void>;
+
+	/**
+	 * Supports registering a handler to run during kernel change and implement any calls needed to configure
+	 * the kernel before actions such as run should be allowed
+	 */
+	onKernelChanging(changeHandler: ((kernel: nb.IKernelChangedArgs) => Promise<void>)): void;
 }
 
 export interface IDefaultConnection {
@@ -322,7 +330,7 @@ export interface INotebookModel {
 	/**
 	 * Change the current context (if applicable)
 	 */
-	changeContext(host: string, connection?: IConnectionProfile): void;
+	changeContext(host: string, connection?: IConnectionProfile): Promise<void>;
 
 	/**
 	 * Find a cell's index given its model
@@ -400,7 +408,10 @@ export interface ICellModel {
 	readonly future: FutureInternal;
 	readonly outputs: ReadonlyArray<nb.ICellOutput>;
 	readonly onOutputsChanged: Event<ReadonlyArray<nb.ICellOutput>>;
+	readonly onExecutionStateChange: Event<boolean>;
 	setFuture(future: FutureInternal): void;
+	readonly isRunning: boolean;
+	runCell(notificationService?: INotificationService): Promise<boolean>;
 	equals(cellModel: ICellModel): boolean;
 	toJSON(): nb.ICellContents;
 }