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/RCTShadowRawText.m

@@ -9,8 +9,32 @@
 
 #import "RCTShadowRawText.h"
 
+#import "RCTUIManager.h"
+
 @implementation RCTShadowRawText
 
+- (instancetype)init
+{
+  if ((self = [super init])) {
+    [[NSNotificationCenter defaultCenter] addObserver:self
+                                             selector:@selector(contentSizeMultiplierDidChange:)
+                                                 name:RCTUIManagerWillUpdateViewsDueToContentSizeMultiplierChangeNotification
+                                               object:nil];
+  }
+  return self;
+}
+
+- (void)dealloc
+{
+  [[NSNotificationCenter defaultCenter] removeObserver:self];
+}
+
+- (void)contentSizeMultiplierDidChange:(NSNotification *)note
+{
+  [self dirtyLayout];
+  [self dirtyText];
+}
+
 - (void)setText:(NSString *)text
 {
   if (_text != text) {