Notebook views UI 2 (#15865)

Provide access to the Notebook Views UI. Feature is hidden behind a feature flag.

Co-authored-by: rkselfhost <rkselfhost@outlook.com>

src/sql/workbench/services/notebook/common/contracts.ts

@@ -45,8 +45,10 @@ export enum NotebookChangeType {
 	MetadataChanged,
 	TrustChanged,
 	Saved,
+	CellExecutionStarted,
 	CellExecuted,
 	CellInputVisibilityChanged,
+	CellAwaitingInput,
 	CellOutputCleared,
 	CellMetadataUpdated
 }