Test & document Visibility Control Header with static built libraries

[lilustga]

Test a change to the Symbol Visibility Control Header to accommodate building code as a static library. The export macros will be blank in the case of a static library.

The change is discussed in this comment thread: https://github.com/ms-iot/ROSOnWindows/pull/322#discussion_r595002284

[traversaro]

To clarify, I usually suggest to support the static usecase for standalone libraries so that they can be easily packaged inside vcpkg (https://github.com/Microsoft/vcpkg) for all the official supported triplets.

[ooeygui]

https://ms-iot.github.io/ROSOnWindows/Porting/SymbolVisibility.html

[ooeygui]

We need to move our symbol visibility doc to ROS.org. And add the CMake doc

[IoTDan]

fixed - documented and published