Some tests are already supported on "remote" devices and simulators.
However, there is currently no way to distinguish a remote macOS host
from a local one.
This adds the darwin-remote feature which is common to all test targets
which use a wrapper script (e.g. iossim_run.py).
rdar://167735355
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Co-authored-by: Dan Blackwell <danblackwell95@gmail.com>