Update types for contact fields that may be null

[thisjeremiah]

It seems that givenName and familyName could be null for fetched contacts on Android devices. This possibility is not reflected in the current TS types.

This scenario can be reproduced by creating a contact with no name and only an "important date" (eg birthday) on Android.

If this doesn’t seem like a bug in the implementation, I can make a PR to update the typings for these fields.

[morenoh149]

@thisjeremiah please submit a pr updating the typings