add iwyu mappings for gtest and gmock

  { include: [ "<bits/types/struct_rusage.h>", private, "<sys/resource.h>", public ] },

  { include: [ "<bits/exception.h>", public, "<exception>", public ] },

  { include: [ "@<Eigen/.*>", private, "<Eigen/Eigen>", public ] },

  { include: [ "@\"gtest/.*\"", private, "\"gtest/gtest.h\"", public ] },

  { include: [ "@\"gmock/.*\"", private, "\"gmock/gmock.h\"", public ] },

]