Fix uncontrolled multiline TextInput not resizing when children change

## Summary

When a multiline TextInput uses children (attributed text) instead of the
`value` prop (uncontrolled mode), changing the children does not cause the
TextInput to resize. For example, clearing children after sending a message
leaves the input at its expanded multi-line height.

## Root Cause

`measureContent()` is called by Yoga during `YGNodeCalculateLayout`, which
runs BEFORE `updateStateIfNeeded()` in the `layout()` callback. In
`attributedStringBoxToMeasure()`, when the state is meaningful and the
`attributedStringBox` is non-empty, it returns the stale native text for
measurement — even though the React tree (children) has already changed.

The sequence:
1. User types multiline text → native `_updateState()` updates
   `attributedStringBox` with the typed text
2. User clears text (e.g. sends message) → React children become empty
3. Yoga calls `measureContent()` → `attributedStringBoxToMeasure()` returns
   the stale multi-line text → height stays expanded
4. `updateStateIfNeeded()` runs later and updates state, but the layout
   has already been computed with the wrong size

## Fix

In `attributedStringBoxToMeasure()`, check if the React tree attributed
string has diverged from what's stored in state. If so, use the React tree
version for measurement instead of the stale `attributedStringBox`. This
ensures Yoga measures with the correct content when children change between
layout passes.

## Changelog
[iOS][Fixed] - Fix uncontrolled multiline TextInput not resizing when children change

Fixes #54570

Author: janicduplessis

packages/react-native/ReactCommon/react/renderer/components/textinput/BaseTextInputShadowNode.h

@@ -204,6 +204,24 @@ class BaseTextInputShadowNode
             layoutContext.fontSizeMultiplier;
     if (meaningfulState) {
       const auto &stateData = BaseShadowNode::getStateData();
+
+      // Check if the react tree has changed since the last state update.
+      // This happens with uncontrolled TextInputs where native text differs
+      // from what React children produce (e.g. after clearing text on send).
+      // In that case, measureContent() is called by Yoga before
+      // updateStateIfNeeded() runs (which happens in layout(), after
+      // YGNodeCalculateLayout), so stateData.attributedStringBox still
+      // contains the stale native text. Use the react tree for measurement
+      // instead to get the correct size.
+      const auto &reactTreeAttributedString = getAttributedString(layoutContext);
+      if (!stateData.reactTreeAttributedString.isContentEqual(reactTreeAttributedString)) {
+        auto attributedString = reactTreeAttributedString;
+        if (attributedString.isEmpty()) {
+          attributedString = getPlaceholderAttributedString(layoutContext);
+        }
+        return AttributedStringBox{attributedString};
+      }
+
       auto attributedStringBox = stateData.attributedStringBox;
       if (attributedStringBox.getMode() == AttributedStringBox::Mode::OpaquePointer ||
           !attributedStringBox.getValue().isEmpty()) {