(iOS) Support for ExtraBold alias of Heavy (font-weight 800)

Summary:
ExtraBold is a fairly common suffix in font naming. A good example is "Circe-ExtraBold". It's usually synonymous with Heavy or Black at font weight 800, as described here: https://www.webtype.com/info/articles/fonts-weights/

This fixes a regression with ExtraBold fonts introduced in d3007b0 where simply having an extrabold font will cause `weightOfFont` to choose this weight aggressively, resulting in all bold text erroneously interpreted as extrabold/heavy. This fix ensures that extrabold is detected before bold, and correctly attributed to `UIFontWeightHeavy`.
Closes #16323

Differential Revision: D6119059

Pulled By: shergin

fbshipit-source-id: 56a5c30584f220974308a7d6068c8d952aa20fb8

React/Views/RCTFont.mm

@@ -51,6 +51,7 @@ static RCTFontWeight weightOfFont(UIFont *font)
       @"medium",
       @"semibold",
       @"demibold",
+      @"extrabold",
       @"bold",
       @"heavy",
       @"black"
@@ -64,6 +65,7 @@ static RCTFontWeight weightOfFont(UIFont *font)
       @(UIFontWeightMedium),
       @(UIFontWeightSemibold),
       @(UIFontWeightSemibold),
+      @(UIFontWeightHeavy),
       @(UIFontWeightBold),
       @(UIFontWeightHeavy),
       @(UIFontWeightBlack)