debugger: Add an action to rerun the last session (#31442)

This works the same as selecting the first history match in the new
session modal.

Release Notes:

- Debugger Beta: Added the `debugger: rerun last session` action, bound
by default to `alt-f4`.

crates/project/src/task_inventory.rs

@@ -230,6 +230,10 @@ impl Inventory {
         }
     }
 
+    pub fn last_scheduled_scenario(&self) -> Option<&DebugScenario> {
+        self.last_scheduled_scenarios.back()
+    }
+
     pub fn list_debug_scenarios(
         &self,
         task_contexts: &TaskContexts,