cmake: fix sat/java/CMakeLists.txt

note:
* need to introduce a new target `java_cp_model_proto` which depends on the
custom cmd generating the java/cp_model_proto.swig
* then use SWIG_MODULE_jnicp_model_proto_EXTRA_DEPS to force generation of it.
ref: https://cmake.org/cmake/help/latest/module/UseSWIG.html#cmake-variables