Dynamic Text Sizes for Text component

Summary:
Dynamic Text Sizes for Text component.
Text gains new prop - allowFontScaling (true by default).
There is also AccessibilityManager module that allows you to tune multipliers per each content size category, but predefined multipliers are there.
This could potentially break some apps so please test carefully.

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) {