feat(Android, Tabs): integrate with ScrollViewMarker for special effects

[kkafar]

Description

Repeated selection of the already-active tab runs "special effects" — pop the
stack to root and/or scroll the content to the top. Until now the scroll view
backing the scroll-to-top effect was located purely by walking the first
descendant of the tab content, which is fragile and only ever matched
android.widget.ScrollView.

This PR integrates that lookup with the ScrollViewMarker mechanism: a marker
mounted around the content's scroll view registers it with the nearest seeking
ancestor, giving the tab a reliable handle to the correct scroll view instead
of relying solely on tree traversal. It also adds NestedScrollView support.

Closes https://github.com/software-mansion/react-native-screens-labs/issues/1538
Closes https://github.com/software-mansion/react-native-screens-labs/issues/1423

Note

The pop-to-root is not-yet-implemented due to modal constraints. It requires changes in the tabs model (simplifying here).

Changes

• TabsScreen now implements ScrollViewSeeking; it stores the scroll view
  registered by a ScrollViewMarker in a WeakReference and exposes it via
  contentScrollView().
• SpecialEffectsHandler resolves the content scroll view from the registered
  marker first, falling back to the descendant-chain search. Both
  repeated-selection effects (pop-to-root and scroll-to-top) now anchor on the
  selected TabsScreen rather than the container content view.
• Scroll-to-top now handles both ScrollView and NestedScrollView.
• ViewFinder.findScrollViewInFirstDescendantChain widened to return
  ViewGroup? and match NestedScrollView, so the fallback path can resolve
  it too.

Visual docs

before	after
android-tabs-special-effects-before.mov	android-tabs-special-effects-after.mov

Test plan

Tested on Android via the example app scenario:
apps/src/tests/component-integration-tests/scroll-view-marker/test-stack-svm-tabs-special-effects/

Steps:

1. Open the scenario, select a tab, scroll its content down and/or push screens
   onto the stack.
2. Tap the already-selected tab again.
3. Verify the stack pops to root and the content smoothly scrolls to the top,
   for both ScrollView- and NestedScrollView-backed content.

Checklist

• Included code example that can be used to test this change.
• For visual changes, included screenshots / GIFs / recordings documenting the change.
• For API changes, updated relevant public types.
• Ensured that CI passes

[Copilot]

Pull request overview

This PR improves Android Tabs “repeated selection” special effects by integrating tab content scroll-to-top behavior with the ScrollViewMarker registration mechanism, making the scroll view lookup more reliable and adding NestedScrollView support.

Changes:

• TabsScreen now participates in the ScrollViewMarker mechanism by implementing ScrollViewSeeking and storing a weak reference to the registered content scroll view.
• Repeated-selection special effects now resolve the scroll view via marker registration first, then fall back to the existing descendant-chain search.
• The fallback scroll-view search and smooth-scroll behavior now support both ScrollView and NestedScrollView.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
android/src/main/java/com/swmansion/rnscreens/gamma/tabs/screen/TabsScreen.kt	Makes the selected tab screen capable of receiving a registered scroll view reference from ScrollViewMarker.
android/src/main/java/com/swmansion/rnscreens/gamma/tabs/container/TabsContainer.kt	Updates repeated-selection effects to target the selected TabsScreen and adds scroll view resolution + NestedScrollView scrolling support.
android/src/main/java/com/swmansion/rnscreens/gamma/helpers/ViewFinder.kt	Expands the fallback “first descendant chain” lookup to match NestedScrollView and returns ViewGroup?.

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[kmichalikk]

Instead of ViewGroup, you could use FrameLayout which is closer to the actual classes

Also, gemini came up with sth like that

interface ScrollableContainer {
    fun scrollToTop()
}

// Extension functions to easily wrap them
fun ScrollView.asScrollable() = object : ScrollableContainer {
    override fun scrollToTop() = smoothScrollTo(0, 0)
}

fun NestedScrollView.asScrollable() = object : ScrollableContainer {
    override fun scrollToTop() = smoothScrollTo(0, 0)
}

this is probably overkill, but you could make the typing more strict this way

[kmichalikk]

maybe region / endregion instead?