When the datepicker UI is shown and then destroyed programmatically:
```js
$( "#datepicker" ).datepicker( "destroy" );
```
hide the datepicker UI without the need for an explicit user action.
Previously, in 1.12 the UI would not disappear immediately but only after the
first `mousedown`. In later 1.13 versions, the UI would not disappear at all.
Fixes gh-2178
Closes gh-2268
This helps fix issues that make tooltip tests sometimes fail when run against
jQuery 3.2 or newer due to timing differences.
Details:
* Add the `moduleAfterEach` function ensuring no timers are running.
* Attach this function via `common.testWidget`.
* Attach this function to most test suites.
* Add a tooltip test helper cleaning up leftover timers.
* Rename legacy `setup`/`teardown` hooks to `beforeEach`/`afterEach`.
Closes gh-1920
