Stop reading buttons back out of the pointer payload under construction (#58297)

Summary:
Pull Request resolved: #58297

`PointerEvent.createW3CPointerEvent` built its payload map, then read one field
straight back out of that same half-built map to compute another field:

```
pointerEvent.putInt("buttons", getButtons(_eventName, pointerType, buttonState))
...
getPressure(pointerEvent.getInt("buttons"), _eventName)
```

Reading from a `WritableNativeMap` while still writing to it is not free and not
safe:

- `ReadableNativeMap.getInt` materialises the *whole* map across JNI
  (`importKeys` + `importValues`) and memoises the result in `keysStorage` /
  `localMapStorage`. Every subsequent `put*` on the same instance then leaves
  those caches stale, so a later Kotlin-side read of the map (`hasKey`,
  `toHashMap`) does not see `pressure`, `tangentialPressure`,
  `hitPathForEventListener` or the modifier keys.
- It happens on the pointer-event hot path, once per pointer index per dispatch,
  purely to recover a value the caller already has in hand.

Keep the value in a local and pass it to `getPressure` directly. The payload is
byte-for-byte identical: `getInt` returns exactly the `Int` that `putInt` stored,
so `getPressure` receives the same argument as before.

Changelog:
[Internal]

Reviewed By: christophpurrer

Differential Revision: D118471070

fbshipit-source-id: 79b06256e8e6e245bcd050a5faa666202fa7a068

Author: generatedunixname1608173377072046

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/events/PointerEvent.kt

@@ -204,13 +204,14 @@ internal class PointerEvent private constructor() : Event<PointerEvent>() {
         "button",
         getButtonChange(pointerType, eventState.lastButtonState, buttonState),
     )
-    pointerEvent.putInt("buttons", getButtons(_eventName, pointerType, buttonState))
+    val buttons = getButtons(_eventName, pointerType, buttonState)
+    pointerEvent.putInt("buttons", buttons)
 
     val pressure =
         if (isClickEvent) {
           0.0 // click events need pressure=0
         } else {
-          getPressure(pointerEvent.getInt("buttons"), _eventName)
+          getPressure(buttons, _eventName)
         }
 
     pointerEvent.putDouble("pressure", pressure)