Add saved and executed events to notebook changed (#5848)

- Updated the notebook API to add a change kind, and support saved, executed and other simplified status
- Plumbed this through to the main thread classes
- Support sending the events from cell / input to the notebook model so they loop over the extension host as a content changed event
- Add executed event from the cell

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

@@ -645,4 +645,11 @@ export enum ColumnType {
 export enum ActionOnCellCheckboxCheck {
 	selectRow = 0,
 	customAction = 1
+}
+
+export enum NotebookChangeKind {
+	ContentUpdated = 0,
+	MetadataUpdated = 1,
+	Save = 2,
+	CellExecuted = 3
 }