This reverts commit 5257f029.

* Building shared C source code as part of the native build for platforms Android, iOS, Linux desktop, MacOS desktop, and Windows desktop.
* Sample code doing a synchronous FFI call.
* Sample code doing a long running synchronous FFI call on a helper isolate.
* Use of `package:ffigen` to generate the bindings.

Check in linux and windows platform code now that they are stable, so that we could use in devicelab in the future. Removed the ICO from the windows example to avoid analysis check, and since it won't be important for benchmarking or UI tests