Summary:
This PR fixes a crash when opening the Performance Monitor on iOS 13.4.
Detailed info: https://github.com/facebook/react-native/issues/28414

## Changelog

`[iOS] [Fixed] - Fix crash when enabling Performance Monitor on iOS 13.4`

## How

This PR prevents the JavaScriptCore option from being set altogether.
This ensures that the performance monitor keeps working, but on iOS 13.4 and higher, it will no longer crash trying to show the GC usage.
Pull Request resolved: https://github.com/facebook/react-native/pull/28512

Test Plan:
Tested on iOS 13.4 (simulator):

![image](https://user-images.githubusercontent.com/6184593/77903803-c6370c00-7283-11ea-8b71-b6b6546c82f6.png)

Tested on iOS 13.1 (simulator)

![image](https://user-images.githubusercontent.com/6184593/77903499-41e48900-7283-11ea-9d14-83f67a3b7b77.png)

- Verified that the `setOption` was called, but the Performance Monitor didn't show any GC usage regardless.
- Identical PR https://github.com/expo/react-native/pull/21 has been shipped and tested in Expo Client 37

Fixes https://github.com/facebook/react-native/issues/28414

Reviewed By: PeteTheHeat

Differential Revision: D20851131

Pulled By: TheSavior

fbshipit-source-id: ff96301036e8487db59f95947bbe6841fe230e1e