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/bundle_adjustment_test_util.h

@@ -37,6 +37,7 @@
 #include <cstdlib>
 #include <string>
 
+#include "absl/log/log.h"
 #include "ceres/autodiff_cost_function.h"
 #include "ceres/internal/export.h"
 #include "ceres/ordered_groups.h"
@@ -46,7 +47,6 @@
 #include "ceres/stringprintf.h"
 #include "ceres/test_util.h"
 #include "ceres/types.h"
-#include "glog/logging.h"
 
 namespace ceres {
 namespace internal {