Add option to enable/disable EXC_BAD_ACCESS suppression

[jamescrosswell]

In #3909 we added some code to suppress EXC_BAD_ACCESS mach exceptions in the CocoaSDK, as these frequently duplicate a managed NullReferenceException.

We did some similar work in #3903 on Android. However for Android we added an option to let SDK users enable/disable suppression. For consistency, I think we should add a similar option to control EXC_BAD_ACCESS suppression.

As with the Android functionality, this will also need documenting. Possibly we could create some shared documentation explaining the necessity for the existence of this functionality and then some platform specific stuff detailing how to enable/disable it on iOS/Android.