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/linear_solver/samples/basic_example.py

@@ -17,6 +17,7 @@
 # [START import]
 from ortools.init.python import init
 from ortools.linear_solver import pywraplp
+
 # [END import]