Fix imobiledevice backend: Check API version for DEVICE_PAIRED
Add an API-version definition to consumers of the imobiledevice imported target. The definition is not very fine-grained, but right now it's enough to distinguish "1.3.0" from "not-1.3.0" releases. A better approach would unpack the version string returned from pkg-config into suitable hex values.
The value of IMOBILEDEVICE_API is a (hex) constant consisting of (major<<16)|(minor<<8)|patch, in order to be compatible with QT_VERSION_CHECK, so 1.3.0 becomes 0x10300.
In the imobiledevice backend, restore the code that does
nothing with DEVICE_PAIRED, but now protect it with versioning
#ifdefs
and restore the unhandled-event warning.