Take abseil as a dependency

1. Add abseil-cpp as a submodule. We are tracking the latest LTS
release, which is lts_2024_01_16.
2. Replace glog/gflags with absl::log and absl::flags.
3. Remove miniglog
4. Also take a whack at making the bazel build work with
   abseil-cpp and gtest.

There are a number of TODOs in this CL that still need to be resolved.

Change-Id: I39355ed7d61375be4ebcbc8596d9cc70acc1c678

examples/rosenbrock_numeric_diff.cc

@@ -33,8 +33,10 @@
 // GradientProblemSolver using derivatives computed using numeric
 // differentiation.
 
+#include <iostream>
+
+#include "absl/log/initialize.h"
 #include "ceres/ceres.h"
-#include "glog/logging.h"
 
 // f(x,y) = (1-x)^2 + 100(y - x^2)^2;
 struct Rosenbrock {
@@ -55,7 +57,7 @@ struct Rosenbrock {
 };
 
 int main(int argc, char** argv) {
-  google::InitGoogleLogging(argv[0]);
+  absl::InitializeLog();
 
   double parameters[2] = {-1.2, 1.0};