Add docstring for the new disposed signal

src/debugger.ts

@@ -128,6 +128,22 @@ export namespace Debugger {
     readonly variablesModel: Variables.Model;
     readonly connector: IDataConnector<ReadonlyJSONValue> | null;
 
+    dispose(): void {
+      this._isDisposed = true;
+      this._disposed.emit();
+    }
+
+    /**
+     * A signal emitted when the debugger widget is disposed.
+     */
+    get disposed(): ISignal<this, void> {
+      return this._disposed;
+    }
+
+    get isDisposed(): boolean {
+      return this._isDisposed;
+    }
+
     get mode(): IDebugger.Mode {
       return this._mode;
     }
@@ -144,10 +160,6 @@ export namespace Debugger {
       return this._modeChanged;
     }
 
-    get isDisposed(): boolean {
-      return this._isDisposed;
-    }
-
     get codeValue() {
       return this._codeValue;
     }
@@ -156,15 +168,6 @@ export namespace Debugger {
       this._codeValue = observableString;
     }
 
-    get disposed(): ISignal<this, void> {
-      return this._disposed;
-    }
-
-    dispose(): void {
-      this._isDisposed = true;
-      this._disposed.emit();
-    }
-
     private async _populate(): Promise<void> {
       const { connector } = this;