Support passing unserializable props to custom button (#2192)

This commit applies the save props mechanism used when pushing screen
to navigator buttons as well, enabling us to pass unserializable props to buttons.

src/deprecated/platformSpecificDeprecated.ios.js

       navigatorButtons,
       navigatorEventID
     } = _mergeScreenSpecificSettings(tab.screen, screenInstanceID, tab);
+    _processNavigatorButtons(navigatorButtons);
     tab.navigationParams = {
       screenInstanceID,
       navigatorStyle,
     navigatorButtons,
     navigatorEventID
   } = _mergeScreenSpecificSettings(screen.screen, screenInstanceID, screen);
+  _processNavigatorButtons(navigatorButtons);
   params.navigationParams = {
     screenInstanceID,
     navigatorStyle,
     navigatorButtons,
     navigatorEventID
   } = _mergeScreenSpecificSettings(params.screen, screenInstanceID, params);
+  _processNavigatorButtons(navigatorButtons);
   const passProps = Object.assign({}, params.passProps);
   passProps.navigatorID = navigator.navigatorID;
   passProps.screenInstanceID = screenInstanceID;
     navigatorButtons,
     navigatorEventID
   } = _mergeScreenSpecificSettings(params.screen, screenInstanceID, params);
+  _processNavigatorButtons(navigatorButtons);
   const passProps = Object.assign({}, params.passProps);
   passProps.navigatorID = navigator.navigatorID;
   passProps.screenInstanceID = screenInstanceID;
 }
 
 function navigatorSetButtons(navigator, navigatorEventID, params) {
+  _processNavigatorButtons(params);
   if (params.leftButtons) {
     const buttons = params.leftButtons.slice(); // clone
     for (let i = 0; i < buttons.length; i++) {
     navigatorButtons,
     navigatorEventID
   } = _mergeScreenSpecificSettings(params.screen, screenInstanceID, params);
+  _processNavigatorButtons(navigatorButtons);
   const passProps = Object.assign({}, params.passProps);
   passProps.navigatorID = navigatorID;
   passProps.screenInstanceID = screenInstanceID;
   return await ScreenUtils.getCurrentlyVisibleScreenId();
 }
 
+function _processNavigatorButtons({rightButtons, leftButtons}) {
+  _saveNavigatorButtonsPassProps(rightButtons);
+  _saveNavigatorButtonsPassProps(leftButtons);
+}
+
+function _saveNavigatorButtonsPassProps(buttons = []) {
+  buttons.forEach((button) => {
+    if (button.component) {
+      const passPropsKey = _.uniqueId('customButtonComponent');
+      PropRegistry.save(passPropsKey, button.passProps);
+      button.passProps = {passPropsKey};
+    }
+  })
+}
+
 export default {
   startTabBasedApp,
   startSingleScreenApp,