IssueTracker

Its necessary to be able to observe wether the system is currently handling a back gesture.

Take for example a scrollbar on the edge of the screen as seen in the following [PR](https://github.com/android/nowinandroid/pull/722) in Now in Android.

We would like to hide the scrollbar if the system back is being triggered. We do not want to use the [systemGestureExclusion](https://developer.android.com/reference/kotlin/androidx/compose/foundation/package-summary#(androidx.compose.ui.Modifier).systemGestureExclusion()) API for this as it would mean disabling back on the edges where the scrollbar is present.

While the [OnBackPressedDispatcher.hasEnabledCallbacks()](https://developer.android.com/reference/androidx/activity/OnBackPressedDispatcher#hasEnabledCallbacks()) API imperatively lets one know if the system is currently consuming a back gesture, we cannot react to it to change the UI without polling.

This API could also report the progress of the back gesture in case the UI wanted to update itself based on this as well.