feat(ios): support custom scale property in ImageParser

[IsaacIsrael]

Summary

When an image source dictionary includes a scale key, ImageParser now re-creates the UIImage at the requested scale factor. This enables callers to pass { uri, scale } to precisely control how tab-bar and toolbar icons render on high-DPI displays — without relying on @2x/@3x filename suffixes, which are unavailable for dynamically downloaded images (e.g. avatars fetched from a CDN at runtime).

Problem

React Native Navigation uses [RCTConvert UIImage:] to parse image sources, which defaults to scale = 1.0 for URI-based images. On Retina displays, this causes dynamically downloaded images to render at their full pixel size instead of the intended logical size. The standard @2x/@3x suffix convention doesn't apply to images downloaded to the cache directory at runtime.

Solution

After the existing image parsing logic, check whether the source dictionary contains a scale key. If present (and > 0), re-create the UIImage with the specified scale using [UIImage imageWithCGImage:scale:orientation:]. This is safe, backwards-compatible, and only activates when the caller explicitly opts in.

Usage

Navigation.mergeOptions(componentId, {
  bottomTabs: {
    children: [{
      options: {
        bottomTab: {
          icon: { uri: 'file:///path/to/avatar.png', scale: 3 }
        }
      }
    }]
  }
});

Test plan

• Verified with dynamically downloaded tab-bar avatar icons at scale: 2 and scale: 3
• Confirmed existing image sources (without scale key) are unaffected
• Confirmed system images ({ system: 'star' }) bypass the scale logic

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