[macOS] Fix `Fling` not sending touch events and begin/end states consistently (#4395)

## Description

The macOS `Fling` recognizer is a separate `NSGestureRecognizer`
implementation with several gaps compared to its iOS counterpart:

- it never fed `pointerTracker`, so `onTouches*` callbacks never fired;
- it never dispatched BEGAN itself — on successful flicks `onBegin` only
arrived at activation time (AppKit coerces the recognizer's `Possible →
Changed` transition into `Began` first, which accidentally supplies it
mid-drag instead of at touch-down);
- failed gestures (click, slow drag, too-slow flick) produced no events
at all — no `onBegin`, no `onFinalize` — breaking the begin/finalize
pairing, because the fail path fires no action and there was no `reset`
override to deliver the final state;
- it never set the pointer type.

All of this is now mirrored from the iOS recognizer: tracker calls in
`mouseDown`/`mouseDragged`/`mouseUp`, a BEGAN `triggerAction` on
mouse-down, a `reset` override with `triggerActionFromReset`, and
`setCurrentPointerTypeToMouse`.

Touch-event delivery on macOS additionally requires #4390 (pointer
tracker matching `NSEvent`s); there is no code dependency between the
two PRs.

## Test plan

Tested in `macos-example` (with #4390 merged locally) using a v3
`useFlingGesture` with all state and touch callbacks:

- fast flick: `onTouchesDown` → `onBegin` → `onTouchesMove`s →
`onActivate` → `onTouchesUp` → `onDeactivate` → `onFinalize
canceled=false`;
- slow drag: fails via the max-duration timer, `onFinalize
canceled=true` (previously: no events at all);
- plain click: `onTouchesDown` → `onBegin` → `onTouchesUp` → `onFinalize
canceled=true` (previously: no events at all);
- repeated gestures behave identically (reset works).

In the timer-fail path `onTouchesCancel` arrives after `onFinalize` —
the same reset ordering the iOS recognizer produces.