Fix scaleBarEnabled on new arch

[janicduplessis]

Description

This fixes scaleBarEnabled={false} on new arch. RNMBXConvertFollyDynamicToId converts to NSBoolean * so when assigning to a Bool prop it is always true. To fix it I used the RNMBX_OPTIONAL_PROP_BOOL macro which handles deferencing the pointer properly.

Tested in an app using new arch, before the change the scale bar is always visible even when setting scaleBarEnabled={false}. After the scale bar is properly hidden.

Checklist

• I've read CONTRIBUTING.md
• I updated the doc/other generated code with running yarn generate in the root folder
• I have tested the new feature on /example app.
  • In V11 mode/ios
  • In New Architecture mode/ios
  • In V11 mode/android
  • In New Architecture mode/android
• I added/updated a sample - if a new feature was implemented (/example)

Screenshot OR Video

Component to reproduce the issue you're fixing

[mfazekas]

@janicduplessis that's great, thanks much!