experimental support for dynamic loading of gurobi; add MPSolver.CreateSolver() factory method for non C++ languages to check correctly installed linear solver backends and licenses when needed; port all non C++ examples

ortools/linear_solver/samples/SimpleLpProgram.java

@@ -30,8 +30,7 @@ public class SimpleLpProgram {
   public static void main(String[] args) throws Exception {
     // [START solver]
     // Create the linear solver with the GLOP backend.
-    MPSolver solver =
-        new MPSolver("SimpleLpProgram", MPSolver.OptimizationProblemType.GLOP_LINEAR_PROGRAMMING);
+    MPSolver solver = MPSolver.createSolver("SimpleLpProgram", "glop");
     // [END solver]
 
     // [START variables]