[Android] Reset the native DOWN flag for unmanaged buttons (#4590)

## Description

`ButtonViewGroup` tracks whether the native dispatch delivered DOWN for
the current gesture and resets it when the handler goes BEGAN. The reset
sat behind the `managedHandlerTag` guard, so it only ran for buttons
that manage their own handler (`Touchable`, `Pressable`). A button
attached through a detector, like `RectButton` with `useNativeGesture`,
set the flag on its first touch and never cleared it. From then on the
#4441 rule degraded to the mid-gesture check only, and a fling caught on
such a button was not cancelled.

The reset now runs before the guard, so every handler on the view gets
the per-gesture rule. Since #4582 the detector rule already covers this
case for detector-attached buttons, so there is no visible change today;
this fixes the stale state so the hook's rule holds on its own.

## Test plan

<details>
<summary>Repro</summary>

```tsx
import { useState } from 'react';
import { FlatList, StyleSheet, Text, View } from 'react-native';
import { GestureHandlerRootView, RectButton } from 'react-native-gesture-handler';

export default function App() {
  const [presses, setPresses] = useState(0);

  return (
    <GestureHandlerRootView style={styles.flex}>
      <Text style={styles.counter}>{`presses=${presses}`}</Text>
      <FlatList
        data={Array.from({ length: 500 }, (_, i) => i)}
        keyExtractor={(item) => String(item)}
        renderItem={({ item }) => (
          <RectButton style={styles.row} onPress={() => setPresses((count) => count + 1)}>
            <Text>Row {item}</Text>
          </RectButton>
        )}
      />
    </GestureHandlerRootView>
  );
}

const styles = StyleSheet.create({
  flex: { flex: 1 },
  counter: { padding: 16, paddingTop: 48, fontFamily: 'monospace' },
  row: { height: 80, justifyContent: 'center', paddingLeft: 16, borderBottomWidth: 1 },
});
```

</details>

Author: m-bert

packages/react-native-gesture-handler/android/src/main/java/com/swmansion/gesturehandler/react/RNGestureHandlerButtonViewManager.kt

@@ -762,6 +762,17 @@ class RNGestureHandlerButtonViewManager :
     }
 
     override fun onHandlerStateChange(handler: NativeViewGestureHandler, newState: Int, prevState: Int) {
+      if (newState == GestureHandler.STATE_BEGAN) {
+        // Reset here, not on gesture end: the native DOWN sets the flag even when the orchestrator
+        // never tracks the handler (disabled button, alpha below the traversal threshold), so a
+        // terminal state may never come and the stale value would survive. BEGAN precedes both the
+        // native dispatch of the same DOWN and the sweep that reads the flag.
+        //
+        // Runs before the managed guard because the sweep reads the flag for detector-attached
+        // buttons too, and those manage no handler.
+        receivedNativeDown = false
+      }
+
       if (managedHandlerTag == null) {
         return
       }
@@ -771,11 +782,6 @@ class RNGestureHandlerButtonViewManager :
       val localLastEventWasInside = lastEventWasInside
 
       if (newState == GestureHandler.STATE_BEGAN) {
-        // Reset here, not on gesture end: the native DOWN sets the flag even when the orchestrator
-        // never tracks the handler (disabled button, alpha below the traversal threshold), so a
-        // terminal state may never come and the stale value would survive. BEGAN precedes both the
-        // native dispatch of the same DOWN and the sweep that reads the flag.
-        receivedNativeDown = false
         flushPendingPressOut()
         pressDownTime = SystemClock.uptimeMillis()
         pressStarted = false