fix(Android, Stack): incorrect header height values (#3402)

## Description

Fixes header height values reported via `onHeaderHeightChange` event.

Fixes
#3040.
Fixes
#2661.

> [!NOTE]
>
> Due to incorrect values being reported previously, there are some
workarounds in `react-navigation`'s `NativeStackView.native.tsx`. Those
should be redundant now and we should clean-up that code when this PR is
merged. We intend to handle backward compatibility through a flag. PR in
`react-navigation`:
react-navigation/react-navigation#12852.

| before | after |
| --- | --- |
| <video
src="https://github.com/user-attachments/assets/b5d2a967-f9d8-480a-9c28-41309f7b8f03"
/> | <video
src="https://github.com/user-attachments/assets/476a044a-352e-42fa-b67a-8d72a4a6f795"
/> |

## Changes

- report height of the header instead of Screen's top offset
- convert px to dp
- update `TestHeaderHeight` to allow testing dynamic changes to the prop
and `react-navigation`'s `useHeaderHeight()` hook

## Test code and steps to reproduce

Run `TestHeaderHeight`.

## Checklist

- [x] Included code example that can be used to test this change
- [x] Ensured that CI passes

Author: kligarski

android/src/main/java/com/swmansion/rnscreens/Screen.kt

@@ -187,9 +187,6 @@ class Screen(
             val height = b - t
 
             dispatchShadowStateUpdate(width, height, t)
-
-            // FormSheet has no header in current model.
-            notifyHeaderHeightChange(t)
         }
     }
 
@@ -458,12 +455,18 @@ class Screen(
             super.onTouchEvent(event)
         }
 
-    private fun notifyHeaderHeightChange(headerHeight: Int) {
+    internal fun notifyHeaderHeightChange(headerHeight: Int) {
         val screenContext = context as ReactContext
         val surfaceId = UIManagerHelper.getSurfaceId(screenContext)
         UIManagerHelper
             .getEventDispatcherForReactTag(screenContext, id)
-            ?.dispatchEvent(HeaderHeightChangeEvent(surfaceId, id, headerHeight))
+            ?.dispatchEvent(
+                HeaderHeightChangeEvent(
+                    surfaceId,
+                    id,
+                    PixelUtil.toDIPFromPixel(headerHeight.toFloat()).toDouble(),
+                ),
+            )
     }
 
     internal fun onSheetDetentChanged(

android/src/main/java/com/swmansion/rnscreens/ScreenStackHeaderConfig.kt

@@ -93,6 +93,8 @@ class ScreenStackHeaderConfig(
                 defaultStartInsetWithNavigation
             }
 
+    val headerHeightUpdateProxy = ScreenStackHeaderHeightUpdateProxy()
+
     fun destroy() {
         isDestroyed = true
     }
@@ -126,6 +128,8 @@ class ScreenStackHeaderConfig(
 
         val contentInsetEnd = toolbar.currentContentInsetEnd + toolbar.paddingEnd
 
+        headerHeightUpdateProxy.updateHeaderHeightIfNeeded(this, screen)
+
         // Note that implementation of the callee differs between architectures.
         updateHeaderConfigState(
             toolbar.width,
@@ -216,6 +220,7 @@ class ScreenStackHeaderConfig(
             if (toolbar.parent != null) {
                 screenFragment?.removeToolbar()
             }
+            headerHeightUpdateProxy.updateHeaderHeightIfNeeded(this, screen)
             return
         }
 
@@ -336,6 +341,8 @@ class ScreenStackHeaderConfig(
             toolbar.addView(view)
             i++
         }
+
+        headerHeightUpdateProxy.updateHeaderHeightIfNeeded(this, screen)
     }
 
     private fun maybeUpdate() {

android/src/main/java/com/swmansion/rnscreens/ScreenStackHeaderHeightUpdateProxy.kt

@@ -0,0 +1,17 @@
+package com.swmansion.rnscreens
+
+class ScreenStackHeaderHeightUpdateProxy {
+    var previousHeaderHeightInPx: Int? = null
+
+    fun updateHeaderHeightIfNeeded(
+        config: ScreenStackHeaderConfig,
+        screen: Screen?,
+    ) {
+        val currentHeaderHeightInPx = if (config.isHeaderHidden) 0 else config.toolbar.height
+
+        if (currentHeaderHeightInPx != previousHeaderHeightInPx) {
+            previousHeaderHeightInPx = currentHeaderHeightInPx
+            screen?.notifyHeaderHeightChange(currentHeaderHeightInPx)
+        }
+    }
+}

android/src/main/java/com/swmansion/rnscreens/events/HeaderHeightChangeEvent.kt

@@ -7,16 +7,16 @@ import com.facebook.react.uimanager.events.Event
 class HeaderHeightChangeEvent(
     surfaceId: Int,
     viewId: Int,
-    private val headerHeight: Int,
+    private val headerHeightInDp: Double,
 ) : Event<HeaderHeightChangeEvent>(surfaceId, viewId) {
     override fun getEventName() = EVENT_NAME
 
     // As the same header height could appear twice, use header height as a coalescing key.
-    override fun getCoalescingKey(): Short = headerHeight.toShort()
+    override fun getCoalescingKey(): Short = headerHeightInDp.toInt().toShort()
 
     override fun getEventData(): WritableMap? =
         Arguments.createMap().apply {
-            putDouble("headerHeight", headerHeight.toDouble())
+            putDouble("headerHeight", headerHeightInDp)
         }
 
     companion object {