Fix custom font weight rendering heaviest face on iOS Fabric (#57483)

Summary:
On the New Architecture (Fabric), a custom font referenced by its PostScript / full font name (e.g. `fontFamily: "Foo-Medium"`) combined with an explicit non-regular `fontWeight` renders at the heaviest available face (bold/black) instead of the requested weight. This is an iOS-only regression introduced in 0.83; 0.82 was correct. Android is unaffected.

**Root cause.** In `RCTFontUtils.mm`, `RCTFontWithFontProperties()` handles the case where the given `fontFamily` is actually a font name rather than a family name (`fontNames.count == 0`) and resolves the effective weight with:

```objc
fontWeight = (fontWeight != 0.0) ?: RCTGetFontWeight(font);
```

`fontWeight` is a `UIFontWeight` (a `double`: Regular = 0.0, Medium = 0.23, Bold = 0.4, Black = 0.62). The Objective-C "Elvis" operator `A ?: B` evaluates to **`A` itself** when `A` is truthy — and here `A` is the *comparison* `(fontWeight != 0.0)`, a `BOOL`. So whenever a weight was set (e.g. 0.23), `fontWeight` was reassigned to `1.0` (heavier than Black), and the subsequent "closest weight in the family" search always picked the heaviest face.

This was introduced by the automated implicit-bool-conversion sweep in #53591 (D81571883), which rewrote the original correct line `fontWeight ?: RCTGetFontWeight(font)` into `(fontWeight != 0.0) ?: …`. Making the truthiness check explicit is fine as a *condition*, but with `?:` the left-hand side is also the *returned value*, so the numeric weight got replaced by the boolean.

**Fix.**

```objc
fontWeight = (fontWeight != 0.0) ? fontWeight : RCTGetFontWeight(font);
```

For a `double`, `(A != 0.0) ? A : B` is exactly equivalent to the original `A ?: B`, so this restores the 0.81/0.82 behavior while keeping the explicit `!= 0.0` form used elsewhere in the file. The no-weight case is unchanged: `RCTResolveFontProperties` fills an unspecified weight with `UIFontWeightRegular` (0.0), so the weight is still inferred from the font name via `RCTGetFontWeight(font)` in that case. The legacy (Paper) path in `React/Views/RCTFont.mm` uses a different construct and is not affected — consistent with his only reproducing on the New Architecture.

## Changelog:

[iOS] [Fixed] - Custom fonts with an explicit fontWeight no longer render at the heaviest weight on the New Architecture

Pull Request resolved: #57483

Test Plan:
Fixes #54934.

New Architecture, iOS, with a custom font bundled and referenced by its PostScript name,
e.g. `<Text style={{ fontFamily: 'Foo-Medium', fontWeight: '500' }}>`:

| Version | Result |
| --- | --- |
| 0.82 | renders at the requested medium weight ✅ |
| 0.83 / `main` (before fix) | renders bold/black ❌ |
| removing `fontWeight` on 0.83 | renders correctly ✅ (confirms the weight branch is the culprit) |

After this change the text renders at the requested weight on both the old and new architecture.

Reviewed By: cortinico

Differential Revision: D111217210

Pulled By: javache

fbshipit-source-id: 76858e1b83f8f1032cb599aec6c4b0d49a6a7427

Author: jensdev

packages/react-native/ReactCommon/react/renderer/textlayoutmanager/platform/ios/react/renderer/textlayoutmanager/RCTFontUtils.mm

@@ -361,7 +361,7 @@ static UIFontDescriptorSystemDesign RCTGetFontDescriptorSystemDesign(NSString *f
       font = [UIFont fontWithName:fontProperties.family size:effectiveFontSize];
       if (font != nullptr) {
         fontNames = [UIFont fontNamesForFamilyName:font.familyName];
-        fontWeight = (fontWeight != 0.0) ?: RCTGetFontWeight(font);
+        fontWeight = (fontWeight != 0.0) ? fontWeight : RCTGetFontWeight(font);
       } else {
         // Failback to system font.
         font = RCTDefaultFontWithFontProperties(fontProperties);