fix(Viewport): allow transitionTo without an explicit transition on iOS

[mfazekas]

Description

Fixes #4226

Viewport.transitionTo(state, transition?) types the transition as optional, and Android already handles a missing transition (falls back to Mapbox's default). On iOS, though, toTransition guarded on the transition's kind and returned nil when it was absent, so transitionTo aborted with a non-descriptive Mapbox [error] no kind found in state and never ran the transition.

This defaults to the default transition when no kind is provided, matching Android and the TypeScript types.

Checklist

• I've read CONTRIBUTING.md
• I updated the doc/other generated code with running yarn generate in the root folder
• I have tested the new feature on /example app.
  • In V11 mode/ios
  • In New Architecture mode/ios
  • In V11 mode/android
  • In New Architecture mode/android
• I added/updated a sample - if a new feature was implemented (/example)

Screenshot OR Video

Verified on the iOS example (New Arch, Mapbox v11). Before the fix, calling transitionTo({ kind: 'followPuck' }) with no transition logged:

Mapbox [error] no kind found in state
Mapbox [error] unable to parse transition in RNMBXViewport.transitionTo

After the fix the transition runs and resolves (transitionTo completed: true); the camera transitions to follow the puck.

Component to reproduce the issue you're fixing

Reproducer

import React, { useEffect, useRef } from 'react';
import { MapView, Viewport } from '@rnmapbox/maps';

function BugReport() {
  const viewportRef = useRef<Viewport>(null);

  useEffect(() => {
    // transition is optional per the TS types; on iOS this previously
    // failed with "no kind found in state" instead of using the default.
    viewportRef.current?.transitionTo({ kind: 'followPuck' });
  }, []);

  return (
    <MapView style={{ flex: 1 }}>
      <Viewport ref={viewportRef} />
    </MapView>
  );
}