added image button as option for accessibility role

Summary:
Because we're now separating accessibilityTraits into accessibilityRole and accessibilityState, we're going to only allow one role to be set, and allow one preset combinations of roles that make sense.

This diff adds image button as a role.

Reviewed By: PeteTheHeat

Differential Revision: D8846958

fbshipit-source-id: dad3783654b20abeb29767cdad7450d1896058c2

Author: Ziqi Chen

Libraries/Components/View/ViewAccessibility.js

@@ -47,7 +47,8 @@ export type AccessibilityRole =
   | 'image'
   | 'keyboardkey'
   | 'text'
-  | 'adjustable';
+  | 'adjustable'
+  | 'imagebutton';
 
 module.exports = {
   AccessibilityTraits: [
@@ -84,5 +85,6 @@ module.exports = {
     'keyboardkey',
     'text',
     'adjustable',
+    'imagebutton',
   ],
 };