mergeOptions for bottomTab broken on iOS

[alex-phillips]

Issue Description

We are issuing the following on a state change to alter the appearance of one of our bottom tabs:

Navigation.mergeOptions('WATCH_TAB', {
  bottomTab: {
    iconColor: 'red',
    textColor: 'red'
  },
});

In version 4, this worked and updated just that tab's color. On iOS in version 6, this is causing the text color to change on ALL tabs (note: the icon color works properly).

Steps to Reproduce / Code Snippets / Screenshots

Issue this command somewhere, we are using it on a state change.

Navigation.mergeOptions(componentId, {
  bottomTab: {
    iconColor: 'red',
    textColor: 'red'
  },
});

---

Environment

• React Native Navigation version: 6.7.2
• React Native version: 0.60.3
• Platform(s) (iOS, Android, or both?): iOS
• Device info (Simulator/Device? OS version? Debug/Release?): This does NOT happen on the simulator, only a device. Seems to be related to iOS 13 as we did not see it on iOS 12. Testing occurred on iPhone 7 running iOS 13.3

[guyca]

@yogevbd could this be related to the Appearance api changes?