Expose shake-to-show dev menu setting via the bridge

Summary:
Apps commonly provide their own rage-shake menus or behaviors, including in dev builds where the dev menu is enabled on shake. Rather than try to override these settings via native code, it can be helpful to let the app define when to show the menu via the bridge.

See recent discussion in https://github.com/facebook/react-native/issues/1054
Closes https://github.com/facebook/react-native/pull/13563

Differential Revision: D4928745

Pulled By: javache

fbshipit-source-id: a5b30e1b198780bb560e1a6d528f727b3b7d4cb7

React/Modules/RCTDevSettings.mm

@@ -202,9 +202,9 @@ RCT_EXPORT_METHOD(reload)
   [_bridge reload];
 }
 
-- (void)setIsShakeToShowDevMenuEnabled:(BOOL)isShakeToShowDevMenuEnabled
+RCT_EXPORT_METHOD(setIsShakeToShowDevMenuEnabled:(BOOL)enabled)
 {
-  [self _updateSettingWithValue:@(isShakeToShowDevMenuEnabled) forKey:kRCTDevSettingShakeToShowDevMenu];
+  [self _updateSettingWithValue:@(enabled) forKey:kRCTDevSettingShakeToShowDevMenu];
 }
 
 - (BOOL)isShakeToShowDevMenuEnabled