Adding back save api (#4407)

* #4339: Kernel change event occurs after model load

* #4347: Code cleanup - Notebooks Save

* Remove save method from sqlops

* Adding save method to api's

* Adding save method to ext host

* Misc change

src/sql/workbench/api/node/mainThreadNotebookDocumentsAndEditors.ts

@@ -77,7 +77,7 @@ class MainThreadNotebookEditor extends Disposable {
 	}
 
 	public save(): Thenable<boolean> {
-		return this.editor.save();
+		return this.editor.notebookParams.input.save();
 	}
 
 	public matches(input: NotebookInput): boolean {