Add try/catch, shim in Nearby initialization

The try/catch allows using a stub NearbyService on branches that do not
support it yet.

Also update Context.NEARBY_SERVICE to ConstantsShim to be compatible
with all branches.

Bug: 189355156
Test: boots
Change-Id: I7db0035b0d9ada79f00d6ef1ac5b54b2e98489d0
1 file changed