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

internal/ceres/visibility.cc

@@ -39,10 +39,11 @@
 #include <utility>
 #include <vector>
 
+#include "absl/log/check.h"
+#include "absl/log/log.h"
 #include "ceres/block_structure.h"
 #include "ceres/graph.h"
 #include "ceres/pair_hash.h"
-#include "glog/logging.h"
 
 namespace ceres::internal {