Tested API_FEM.h functions; added interface functions to ISolver and tested them

Status tests

Added and tested ISolver interface functions

Added and tested ISolver interface functions

Little fix

Change FetchContent to vcpkg in fem/tests'CmakeLists

Change FetchContent to vcpkg in fem/tests'CmakeLists

Changed cmakelist

Removed macro and added workdir; fixed CMakeLists; fixed interface functions in ISolver.h