https://github.com/crossplane/crossplane/tree/b7ce021e32/internal/featurehttps://github.com/crossplane/crossplane/issues/2313.
This is a copy of the (almost) identical crossplane/crossplane package, which
will be removed in favor of this one. Moving to crossplane-runtime allows us to
use the same package in providers, e.g. to disable Alpha APIs per the above
issue.
The package is _almost_ identical because the Flag type has been changed from
int to string. This makes it easier to give flags string names, because the
stringer tool we previously used requires that types and instances be defined in
the same package.
Signed-off-by: Nic Cope <negz@rk0n.org>