Extract out IMobileDevice class, move class to idevice_id, ideviceinfo
(and eventually other libimobiledevice tools such as iproxy) behind this
interface.
Add tests for the case where libimobiledevice is not installed, the case
where it returns no devices, and the case where it returns device IDs.
* Before tests
* Add the part to trust the cert on the device
* flip the error checks since some are more specific and are more actionable
* add tests
* review
Relocates two tests alongside other related tests:
* moved code_signing_test.dart alongside other lib/src/ios tests
* moved terminal_test.dart alongside other lib/src/base tests
