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.

React/Modules/RCTAccessibilityManager.m

@@ -0,0 +1,144 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+#import "RCTAccessibilityManager.h"
+
+#import "RCTLog.h"
+
+NSString *const RCTAccessibilityManagerDidUpdateMultiplierNotification = @"RCTAccessibilityManagerDidUpdateMultiplierNotification";
+
+@interface RCTAccessibilityManager ()
+
+@property (nonatomic, copy) NSDictionary *multipliers;
+@property (nonatomic, copy) NSString *contentSizeCategory;
+@property (nonatomic, assign) CGFloat multiplier;
+
+@end
+
+@implementation RCTAccessibilityManager
+
+@synthesize bridge = _bridge;
+
+RCT_EXPORT_MODULE()
+
++ (NSDictionary *)JSToUIKitMap
+{
+  static NSDictionary *map = nil;
+  static dispatch_once_t onceToken;
+  dispatch_once(&onceToken, ^{
+    map = @{@"extraSmall": UIContentSizeCategoryExtraSmall,
+            @"small": UIContentSizeCategorySmall,
+            @"medium": UIContentSizeCategoryMedium,
+            @"large": UIContentSizeCategoryLarge,
+            @"extraLarge": UIContentSizeCategoryExtraLarge,
+            @"extraExtraLarge": UIContentSizeCategoryExtraExtraLarge,
+            @"extraExtraExtraLarge": UIContentSizeCategoryExtraExtraExtraLarge,
+            @"accessibilityMedium": UIContentSizeCategoryAccessibilityMedium,
+            @"accessibilityLarge": UIContentSizeCategoryAccessibilityLarge,
+            @"accessibilityExtraLarge": UIContentSizeCategoryAccessibilityExtraLarge,
+            @"accessibilityExtraExtraLarge": UIContentSizeCategoryAccessibilityExtraExtraLarge,
+            @"accessibilityExtraExtraExtraLarge": UIContentSizeCategoryAccessibilityExtraExtraExtraLarge};
+  });
+  return map;
+}
+
++ (NSString *)UIKitCategoryFromJSCategory:(NSString *)JSCategory
+{
+  return self.JSToUIKitMap[JSCategory];
+}
+
+- (instancetype)init
+{
+  self = [super init];
+  if (self) {
+    [[NSNotificationCenter defaultCenter] addObserver:self
+                                             selector:@selector(didReceiveNewContentSizeCategory:)
+                                                 name:UIContentSizeCategoryDidChangeNotification
+                                               object:[UIApplication sharedApplication]];
+    self.contentSizeCategory = [[UIApplication sharedApplication] preferredContentSizeCategory];
+  }
+  return self;
+}
+
+- (void)dealloc
+{
+  [[NSNotificationCenter defaultCenter] removeObserver:self];
+}
+
+- (void)didReceiveNewContentSizeCategory:(NSNotification *)note
+{
+  self.contentSizeCategory = note.userInfo[UIContentSizeCategoryNewValueKey];
+}
+
+- (void)setContentSizeCategory:(NSString *)contentSizeCategory
+{
+  if (_contentSizeCategory != contentSizeCategory) {
+    _contentSizeCategory = [contentSizeCategory copy];
+    self.multiplier = [self multiplierForContentSizeCategory:_contentSizeCategory];
+    [[NSNotificationCenter defaultCenter] postNotificationName:RCTAccessibilityManagerDidUpdateMultiplierNotification object:self];
+  }
+}
+
+- (CGFloat)multiplierForContentSizeCategory:(NSString *)category
+{
+  NSNumber *m = self.multipliers[category];
+  if (m.doubleValue <= 0.0) {
+    RCTLogError(@"Can't determinte multiplier for category %@. Using 1.0.", category);
+    m = @1.0;
+  }
+  return m.doubleValue;
+}
+
+- (NSDictionary *)multipliers
+{
+  if (_multipliers == nil) {
+    _multipliers = @{UIContentSizeCategoryExtraSmall: @0.823,
+                     UIContentSizeCategorySmall: @0.882,
+                     UIContentSizeCategoryMedium: @0.941,
+                     UIContentSizeCategoryLarge: @1.0,
+                     UIContentSizeCategoryExtraLarge: @1.118,
+                     UIContentSizeCategoryExtraExtraLarge: @1.235,
+                     UIContentSizeCategoryExtraExtraExtraLarge: @1.353,
+                     UIContentSizeCategoryAccessibilityMedium: @1.786,
+                     UIContentSizeCategoryAccessibilityLarge: @2.143,
+                     UIContentSizeCategoryAccessibilityExtraLarge: @2.643,
+                     UIContentSizeCategoryAccessibilityExtraExtraLarge: @3.143,
+                     UIContentSizeCategoryAccessibilityExtraExtraExtraLarge: @3.571};
+  }
+  return _multipliers;
+}
+
+RCT_EXPORT_METHOD(setAccessibilityContentSizeMultipliers:(NSDictionary *)JSMultipliers)
+{
+  NSMutableDictionary *multipliers = [[NSMutableDictionary alloc] init];
+  for (NSString *__nonnull JSCategory in JSMultipliers) {
+    NSNumber *m = JSMultipliers[JSCategory];
+    NSString *UIKitCategory = [self.class UIKitCategoryFromJSCategory:JSCategory];
+    multipliers[UIKitCategory] = m;
+  }
+  self.multipliers = multipliers;
+}
+
+RCT_EXPORT_METHOD(getMultiplier:(RCTResponseSenderBlock)callback)
+{
+  if (callback) {
+    callback(@[ @(self.multiplier) ]);
+  }
+}
+
+@end
+
+@implementation RCTBridge (RCTAccessibilityManager)
+
+- (RCTAccessibilityManager *)accessibilityManager
+{
+  return self.modules[RCTBridgeModuleNameForClass([RCTAccessibilityManager class])];
+}
+
+@end