Fix empty input accessory button on TextInput without inputAccessoryViewButtonLabel

[jkasprzyk17]

Summary:

Fixes #58952.

With the new architecture, a number-pad TextInput without inputAccessoryViewButtonLabel can show a toolbar with an empty button above the keyboard.

An unset inputAccessoryViewButtonLabel reaches RCTTextInputComponentView as an empty std::string. RCTNSStringFromString("") returns @"", not nil, and setDefaultInputAccessoryView treats any non-nil label as set. The empty string is applied whenever the label goes from set to unset:

• Recycled view: _props still holds the props of the input the view was recycled from. A new input without a label then diffs "Next" → "" and gets @"". Because prepareForRecycle reset _hasInputAccessoryView, a toolbar with an empty button is created.
• Label removed: removing the label from a mounted number-pad input sets @"", and the toolbar keeps the old title.

This change maps an empty label to nil with the existing RCTNSStringFromStringNilIfEmpty helper. This matches the old architecture, where the label was an NSString view property and an unset label was nil. The issue suggests clearing the label in prepareForRecycle, but that isn't enough on its own: the diff against the stale _props would still assign @"".

Changelog:

[IOS] [FIXED] - Fix empty input accessory toolbar on a number-pad TextInput without inputAccessoryViewButtonLabel

Test Plan:

Added RCTTextInputComponentViewTests with four cases:

• a recycled view reused without a label gets no accessory view
• a recycled view reused without a label falls back to the returnKeyType title
• a recycled view reused with a label keeps it
• removing the label removes the accessory view

React/Tests isn't compiled by any open source target, so I couldn't run these tests locally. I did check that the file compiles (-fsyntax-only) with the same clang flags the RNTester build uses for RCTTextInputComponentView.mm.

I tested manually in RNTester (Debug, new architecture, iPhone 17 Pro simulator, iOS 26.5) with this Playground code:

RNTesterPlayground.js

function Playground() {
  const [labelled, setLabelled] = useState(true);
  return (
    <View style={{padding: 10, gap: 8}}>
      <Button
        title={labelled ? 'Swap to unlabelled' : 'Swap to labelled'}
        onPress={() => setLabelled(value => !value)}
      />
      {labelled ? (
        <TextInput
          key="labelled"
          keyboardType="number-pad"
          inputAccessoryViewButtonLabel="Next"
          placeholder='Labelled ("Next")'
        />
      ) : (
        <TextInput
          key="unlabelled"
          keyboardType="number-pad"
          placeholder="Unlabelled"
        />
      )}
    </View>
  );
}

Steps: tap "Swap to unlabelled", then focus the unlabelled input. The new input reuses the recycled view of the labelled one.

Before	After

Before: a toolbar with an empty button above the number pad. After: no toolbar. The labelled input still shows "Next". I also removed the label from a focused number-pad input: the toolbar now goes away.

Commands:

yarn install
yarn --cwd packages/react-native-codegen build
cd packages/rn-tester
pod install
pod update hermes-engine --no-repo-update  # Podfile.lock pinned an older Hermes
cd ../..
xcodebuild -workspace packages/rn-tester/RNTesterPods.xcworkspace -scheme RNTester -configuration Debug \
  -destination 'platform=iOS Simulator,id=<iPhone 17 Pro, iOS 26.5 simulator UDID>' build
# ** BUILD SUCCEEDED **
node scripts/clang-format.js --check \
  packages/react-native/React/Fabric/Mounting/ComponentViews/TextInput/RCTTextInputComponentView.mm \
  packages/react-native/React/Tests/Text/RCTTextInputComponentViewTests.mm
# no output, exit code 0

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