Improve resolveTask documentation

src/vs/vscode.d.ts

@@ -6674,6 +6674,10 @@ declare module 'vscode' {
 		 * tasks are always fully resolved. A valid default implementation for the
 		 * `resolveTask` method is to return `undefined`.
 		 *
+		 * Note that when filling in the properties of `task`, you _must_ be sure to
+		 * use the exact same `TaskDefinition` and not create a new one. Other properties
+		 * may be changed.
+		 *
 		 * @param task The task to resolve.
 		 * @param token A cancellation token.
 		 * @return The resolved task