fontVariant not an allowed title style

[elliottkember]

Hi all!

We're using fontVariant: ['tabular-nums'] for text styling in a header in @react-navigation/native-stack, and I noticed that it's not a respected property. I tried to add it, but got a little stuck on the native part.

I think it'd be great to support tabular numbers, because they look great and are also very useful for IDs or numerical titles. On the JS side, I think it can be added as a titleFontVariant prop, and then it can be passed to RCTFont as the variant property in the native code.

    NSString *variant = config.titleFontVariant ?: nil;
    if (family || weight || variant) {
      attrs[NSFontAttributeName] = [RCTFont updateFont:nil
                                            withFamily:config.titleFontFamily
                                                  size:size
                                                weight:weight
                                                 style:nil
                                               variant:variant
                                       scaleMultiplier:1.0];

On the Android side, I think it's something here, but I'm not familiar enough with this code to know how to change the variant.

                val titleTypeface = ReactTypefaceUtils.applyStyles(
                    null, 0, mTitleFontWeight, mTitleFontFamily, context.assets
                )
                titleTextView.typeface = titleTypeface;

Anyway, thoughts would be appreciated!