Dynamic Text Sizes for Text component

Summary:
Dynamic Text Sizes for Text component.
Text gains new prop - allowFontScaling (false by default).
There is also AccessibilityManager module that allows you to tune multipliers per each content size category.

Libraries/Text/RCTShadowText.h

@@ -30,6 +30,8 @@ extern NSString *const RCTReactTagAttributeName;
 @property (nonatomic, strong) UIColor *textDecorationColor;
 @property (nonatomic, assign) NSUnderlineStyle textDecorationStyle;
 @property (nonatomic, assign) RCTTextDecorationLineType textDecorationLine;
+@property (nonatomic, assign) CGFloat fontSizeMultiplier;
+@property (nonatomic, assign) BOOL allowFontScaling;
 
 - (void)recomputeText;