Add windowSwipeToDismiss attribute in themes_material.xml

We stopped setting the `windowSwipeToDismiss` on main branch. However, if the APP didn't set this attribute explicitly and it's using the AndroidX helper class, the default value will be `false`.
Because the `getIndexCount()` method will return 0. See the code link below.

https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:wear/wear/src/main/java/androidx/wear/utils/WearableNavigationHelper.java;drc=f59de72b8aea152732fc9aa4bb12a61c85d38f01;l=60

This patch set the `windowSwipeToDismiss` attribute to `@empty` so that `getIndexCount()` will not return 0 and the`isSwipeToDismissEnabled()` can correctly override `windowSwipeToDismiss` attribute.



Bug:303796155
Change-Id: Ia0d522e58d686b42a3433f55baaa0ca5fa45081c
Test: manual