Implement Session support through the extension host (#3228)

Full plumb through of Session support. Also fixed some test issues

- Load session and get necessary information in kernels list
- Run Cell button now works as expected
- Added a ToggleAction base class which can be used for anything that switches icons. I'd still prefer to have this be dynamic and as clean as the extension classes
- Fixed account test unhandled promise rejections (caused by incorrect / invalid tests) that made it hard to see all the test run output.

src/sql/workbench/api/common/sqlExtHostTypes.ts

@@ -416,4 +416,39 @@ export interface INotebookManagerDetails {
 	handle: number;
 	hasContentManager: boolean;
 	hasServerManager: boolean;
+}
+
+export interface INotebookSessionDetails {
+	readonly sessionId: number;
+	readonly canChangeKernels: boolean;
+	readonly id: string;
+	readonly path: string;
+	readonly name: string;
+	readonly type: string;
+	readonly status: string;
+	readonly kernelDetails: INotebookKernelDetails;
+}
+
+export interface INotebookKernelDetails {
+	readonly kernelId: number;
+	readonly id: string;
+	readonly name: string;
+	readonly supportsIntellisense: boolean;
+	readonly info?: any;
+}
+
+export interface INotebookFutureDetails {
+	readonly futureId: number;
+	readonly msg: any;
+}
+
+export enum FutureMessageType {
+	Reply = 0,
+	StdIn = 1,
+	IOPub = 2
+}
+
+export interface INotebookFutureDone {
+	succeeded: boolean;
+	rejectReason: string;
 }