Fix #4047 Redesign notebook model to handle single client session (#4371)

* Start single client session based on the default kernel or saved kernel in NB.

* Added kernel displayName to standardKernel.
Modified name to allign wtih Juptyer Kernel.name.
So we can show the displayName during startup and use the name to start the session.

* Change session.OnSessionReady event in KernelDropDown

* Added model.KernelChnaged for switching kernel in the same provider

* Fixed session.Ready sequence

* Fixed merge issues

* Solve merged issue

* Fixed wrong kernel name in saved NB

* Added new event in Model to notify kernel change.
Toolbar depends on ModelReady to load

* Change attachTo to wait for ModelReady like KenelDropDown

* sanitizeSavedKernelInfo to fix invalid kernel and display_name. For example: PySpark1111 and PySpark 1111


* Added _contextsChangingEmitter to change loadContext msg when changing kernel

* Resolve PR comments

src/sql/parts/notebook/notebookUtils.ts

@@ -12,7 +12,6 @@ import * as pfs from 'vs/base/node/pfs';
 import { localize } from 'vs/nls';
 import { IOutputChannel } from 'vs/workbench/parts/output/common/output';
 import { DEFAULT_NOTEBOOK_PROVIDER, DEFAULT_NOTEBOOK_FILETYPE, INotebookService } from 'sql/workbench/services/notebook/common/notebookService';
-import { ContextKeyExpr, IContextKeyService } from 'vs/platform/contextkey/common/contextkey';
 import { ConnectionProfile } from 'sql/platform/connection/common/connectionProfile';
 
 
@@ -97,6 +96,7 @@ export function getDatabaseFromFormattedAttachToName(name: string): string {
 
 export interface IStandardKernelWithProvider {
 	readonly name: string;
+	readonly displayName: string;
 	readonly connectionProviderIds: string[];
 	readonly notebookProvider: string;
 }