Add missing source file, sgen-os-coop.c, to libmonoruntime Visual Studio project.

Add missing source file, sgen-os-coop.c, to libmonoruntime Visual Studio project.

Add missing source file, sgen-os-coop.c to project.

Add source files and headers into correct filters (Header/Source Files).

Eliminated Visual Studio linker warning LNK4221 for libmonoruntime project generated
by empty source files under certain configurations, boehm-gc.c, lock-tracer.c,
null-gc.c and sgen-os-coop.c