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/sampled_function/CMakeLists.txt

@@ -29,4 +29,4 @@
 # Author: vitus@google.com (Michael Vitus)
 
 add_executable(sampled_function sampled_function.cc)
-target_link_libraries(sampled_function PRIVATE Ceres::ceres)
+target_link_libraries(sampled_function PRIVATE absl::log_initialize Ceres::ceres)

examples/sampled_function/sampled_function.cc

@@ -31,9 +31,9 @@
 // A simple example of optimizing a sampled function by using cubic
 // interpolation.
 
+#include "absl/log/initialize.h"
 #include "ceres/ceres.h"
 #include "ceres/cubic_interpolation.h"
-#include "glog/logging.h"
 
 using Interpolator = ceres::CubicInterpolator<ceres::Grid1D<double>>;
 
@@ -59,8 +59,7 @@ struct InterpolatedCostFunctor {
 };
 
 int main(int argc, char** argv) {
-  google::InitGoogleLogging(argv[0]);
-
+  absl::InitializeLog();
   // Evaluate the function f(x) = (x - 4.5)^2;
   const int kNumSamples = 10;
   double values[kNumSamples];