Restart kernel initial implementation (#18835)

* Restart kernel initial implementation

* Update notebook extension TestKernel

* PR comments

src/sql/workbench/contrib/notebook/test/emptySessionClasses.ts

@@ -168,6 +168,10 @@ class EmptyKernel implements nb.IKernel {
 	interrupt(): Thenable<void> {
 		return Promise.resolve(undefined);
 	}
+
+	restart(): Thenable<void> {
+		return Promise.resolve(undefined);
+	}
 }
 
 export class EmptyFuture implements FutureInternal {

src/sql/workbench/contrib/notebook/test/stubs.ts

@@ -353,7 +353,7 @@ export class ClientSessionStub implements IClientSession {
 	selectKernel(): Promise<void> {
 		throw new Error('Method not implemented.');
 	}
-	restart(): Promise<boolean> {
+	restart(): Promise<void> {
 		throw new Error('Method not implemented.');
 	}
 	setPath(path: string): Promise<void> {
@@ -464,6 +464,9 @@ export class KernelStub implements nb.IKernel {
 	interrupt(): Thenable<void> {
 		throw new Error('Method not implemented.');
 	}
+	restart(): Thenable<void> {
+		throw new Error('Method not implemented.');
+	}
 }
 
 export class FutureStub implements nb.IFuture {