Fix inability to remove 'Disabled' state from AccessibilityStates

Summary:
D8842691 split AccessibilityTraits into multiple RN properties.  However, the accessor code did not support REMOVING traits.
This results in buttons that were disabled (AccessibilityTraits & NotEnabled === true) never being enabled.

Fix the issue by making the split accessors properly mask in the bits, allowing you unset them without disturbing bits managed by the other accessor.

NOTE: setting AccessibilityTraits and AccessibilityRole or AccessibilityStates will still result in bugs.

Reviewed By: shergin

Differential Revision: D9661970

fbshipit-source-id: 77d70dd0754f2eaf8cbf895bfc13757c697a76d8

Libraries/Components/View/ViewAccessibility.js

@@ -84,6 +84,7 @@ module.exports = {
     'radiobutton_checked',
     'radiobutton_unchecked',
   ],
+  // This must be kept in sync with the AccessibilityRolesMask in RCTViewManager.m
   AccessibilityRoles: [
     'none',
     'button',
@@ -97,5 +98,6 @@ module.exports = {
     'header',
     'summary',
   ],
+  // This must be kept in sync with the AccessibilityStatesMask in RCTViewManager.m
   AccessibilityStates: ['selected', 'disabled'],
 };