Remove deprecated uses of UIActivityIndicatorViewStyle (facebook#38208)

Summary:
Super simple change to replace some deprecated ENUM values with the correct one, now that we're on iOS 13.0+.

From `UIActivityIndicator.h`:
```
typedef NS_ENUM(NSInteger, UIActivityIndicatorViewStyle) {
    UIActivityIndicatorViewStyleMedium  API_AVAILABLE(ios(13.0), tvos(13.0)) = 100,
    UIActivityIndicatorViewStyleLarge   API_AVAILABLE(ios(13.0), tvos(13.0)) = 101,

    UIActivityIndicatorViewStyleWhiteLarge API_DEPRECATED_WITH_REPLACEMENT("UIActivityIndicatorViewStyleLarge", ios(2.0, 13.0), tvos(9.0, 13.0)) = 0,
    UIActivityIndicatorViewStyleWhite API_DEPRECATED_WITH_REPLACEMENT("UIActivityIndicatorViewStyleMedium", ios(2.0, 13.0), tvos(9.0, 13.0)) = 1,
    UIActivityIndicatorViewStyleGray API_DEPRECATED_WITH_REPLACEMENT("UIActivityIndicatorViewStyleMedium", ios(2.0, 13.0)) API_UNAVAILABLE(tvos) = 2,
};
```

## Changelog:

[IOS] [CHANGED] - Remove deprecated uses of UIActivityIndicatorViewStyle

Pull Request resolved: facebook#38208

Test Plan: CI should pass

Reviewed By: cipolleschi

Differential Revision: D47254035

Pulled By: rshest

fbshipit-source-id: 6d3270899e8d52611d91c777f324c3c6f0c520be

packages/react-native/React/Fabric/Mounting/ComponentViews/ActivityIndicator/RCTActivityIndicatorViewComponentView.mm

@@ -22,9 +22,9 @@ static UIActivityIndicatorViewStyle convertActivityIndicatorViewStyle(const Acti
 {
   switch (size) {
     case ActivityIndicatorViewSize::Small:
-      return UIActivityIndicatorViewStyleWhite;
+      return UIActivityIndicatorViewStyleMedium;
     case ActivityIndicatorViewSize::Large:
-      return UIActivityIndicatorViewStyleWhiteLarge;
+      return UIActivityIndicatorViewStyleLarge;
   }
 }
 

packages/react-native/React/Views/RCTActivityIndicatorViewManager.m

@@ -18,10 +18,10 @@ @implementation RCTConvert (UIActivityIndicatorView)
 RCT_ENUM_CONVERTER(
     UIActivityIndicatorViewStyle,
     (@{
-      @"large" : @(UIActivityIndicatorViewStyleWhiteLarge),
-      @"small" : @(UIActivityIndicatorViewStyleWhite),
+      @"large" : @(UIActivityIndicatorViewStyleLarge),
+      @"small" : @(UIActivityIndicatorViewStyleMedium),
     }),
-    UIActivityIndicatorViewStyleWhiteLarge,
+    UIActivityIndicatorViewStyleLarge,
     integerValue)
 
 @end