backport from main

* rename swig files .i in .swig
* update constraint_solver and routing
* backport math_opt changes
* move dynamic loading to ortools/third_party_solvers

ortools/init/BUILD.bazel

@@ -19,9 +19,9 @@ cc_library(
     hdrs = ["init.h"],
     deps = [
         "//ortools/base",
-        "//ortools/gurobi:environment",
         "//ortools/sat:cp_model_solver",
         "//ortools/sat:cp_model_solver_helpers",
+        "//ortools/third_party_solvers:gurobi_environment",
         "@abseil-cpp//absl/flags:flag",
         "@abseil-cpp//absl/log",
         "@abseil-cpp//absl/log:globals",

ortools/init/init.cc

@@ -20,9 +20,9 @@
 #include "absl/log/globals.h"
 #include "absl/strings/string_view.h"
 #include "ortools/base/init_google.h"
-#include "ortools/gurobi/environment.h"
 #include "ortools/sat/cp_model_solver.h"
 #include "ortools/sat/cp_model_solver_helpers.h"
+#include "ortools/third_party_solvers/gurobi_environment.h"
 
 namespace operations_research {
 void CppBridge::InitLogging(absl::string_view usage) {

ortools/init/java/init.i

@@ -15,7 +15,7 @@
 
 %include "std_string.i"
 
-%include "ortools/util/java/absl_string_view.i"
+%include "ortools/util/java/absl_string_view.swig"
 
 %{
 #include "ortools/init/init.h"

ortools/init/python/init_test.py

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-"""Simple unit tests for python/init.i. Not exhaustive."""
+"""Simple unit tests for python/init.swig. Not exhaustive."""
 
 from absl.testing import absltest
 from ortools.init.python import init