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/evaluation_callback_example.cc

@@ -47,8 +47,9 @@
 #include <iostream>
 
 #include "Eigen/Core"
+#include "absl/log/check.h"
+#include "absl/log/initialize.h"
 #include "ceres/ceres.h"
-#include "glog/logging.h"
 
 // Data generated using the following octave code.
 //   randn('seed', 23497);
@@ -224,7 +225,7 @@ class CostAndJacobianCopyingCostFunction
 };
 
 int main(int argc, char** argv) {
-  google::InitGoogleLogging(argv[0]);
+  absl::InitializeLog();
 
   const double initial_m = 0.0;
   const double initial_c = 0.0;