Add buttons accessibilityLabel support (#5844)

Co-authored-by: Guy Carmeli <guyca@users.noreply.github.com>

lib/ios/RNNNavigationButtons.m

         return nil;
     }
     
+    barButtonItem.accessibilityLabel = dictionary[@"accessibilityLabel"];
     barButtonItem.target = self.viewController;
     barButtonItem.action = @selector(onButtonPress:);
     

lib/src/interfaces/Options.ts

    * Set the button text
    */
   text?: string;
+  /**
+   * Overrides the text that's read by the screen reader when the user interacts with the element
+   */
+  accessibilityLabel?: string;
   /**
    * Set the button font family
    */

playground/src/screens/ButtonsScreen.js

             id: 'LEFT',
             testID: LEFT_BUTTON,
             icon: require('../../img/clear.png'),
-            color: Colors.primary
+            color: Colors.primary,
+            accessibilityLabel: 'Close button'
           }
         ]
       }