* iOS: give long presses the uid of the touch they came from
The long-press recognizer always sent uid 0, while touch uids are `UITouch`
pointers, so a widget matching a long press to the touch it captured never saw
one on iOS. Now the long press carries the uid of the active touch under it.
* StackNavigation: swipe back to the previous view, plus Android predictive back
* A rightward swipe anywhere on a stack view drags it 1:1 and reveals the view beneath,
then on release it either finishes popping or springs back (distance + fling velocity)
* Android's predictive back gesture drives the same reveal via a new `Event::BackGesture`,
and cargo-makepad now opts apps in with `enableOnBackInvokedCallback`
* Only a view that owns Back can be swiped, so modals and popups in front of it block it
* Widgets keep their own drags with `cx.claim_finger_drag()` (`TextInput`, `Slider`, `Splitter`)
* Apps pick the revealed view via `InteractivePop*` actions and `set_interactive_pop_view()`
* Swipe back: leave owned drags, open overlays and UI zoom alone
* The views see each move first, so a scroller that takes the finger (`claim_finger_gesture`)
or a popover that press opened keeps it, and nothing swipes while an overlay holds the pointer
* The slop is in the OS's points, so UI zoom can't make swipes start before long presses do
* Sideways and 2D drags claim their finger: `Toggle`'s knob, horizontal `ScrollBar` thumbs, `Carousel`,
`RangeSlider`, `PlaybackBar`, `Rating`, `ValueInput`, `Kanban`, sideways `WheelPicker`s, FAB controls,
`Video` seeking, `Tab` strips, and the chart, color, glass, waveform, data grid and map widgets
* New `StackNavigationRef::has_pending_interactive_pop()` for apps that handle Back themselves
* Mail, Reminders, Notes, Calculator: follow swipes and back gestures on their stacks
These apps take Back before their UI sees it, so the Back that ends a predictive back gesture
never reached their stack, and a swipe's pop went around their own history. Now they leave Back
to the stack while `has_pending_interactive_pop()`, reveal the screen they'd go back to on
`InteractivePopStarted`, and go back in their own state on `InteractivePopCommitted`. Also
mentions the swipe in the StackNavigation story and the uizoo docs.
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