[IOT-2013] Windows: export C RD APIs from octbstack.dll

[IOT-2013] Windows: export C RD APIs from octbstack.dll

Windows currently has several different copies of the implementation
for these APIs. Other platforms are using a single copy of shared
library resource_directory, in each process/app.

It's better to avoid differences across platforms, because otherwise
changes tested on one platform might not work on the other platforms.

Note that the C++ APIs for resource_directory clients remain inside
the static resource_directory.lib, so there can be multiple copies of
the C++ API implementation in each Windows process.

Change-Id: I07683359c265989d9921cd28da6ccd83d30f06af
Signed-off-by: Dan Mihai <Daniel.Mihai@microsoft.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/18775
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Mike Fenelon <mike.fenelon@microsoft.com>