Rebase mozc onto Abseil logging library.

This is a relatively large update with several breaking changes.

- Most of the code in `//base:logging` is now removed.
- Logging calls are now handled by `@com_google_absl//absl/log`. This means:
  - Log message formats will change.
  - Important: If you have existing log files and run non-release builds (more precisely `!defined(MOZC_NO_LOGGING)`), your files will contain mixed formats after this commit. You may want to remove or rename the existing one.
- Flag deprecations
  - `--colored_log`: they're not supported by Abseil.
  - `--logtostderr`: this flag had a inconsistent behavior with a google-internal flag of the same name (nor it doesn't make sense for mozc to consolidate the semantics), and is not provided by Abseil.
    - Note: There's no longer a way to disable log files in debug builds. A configuration option might be added later if this proves problematic.

The Abseil logging library is packed with many features. It provides out-of-box integration with the Windows debugger and allows you to adjust the verbosity of your logs using command-line flags (e.g., `--stderrthreshold=0` to see all INFO level logs and above). For a full list of features, take a look at their documentation and source code.

PiperOrigin-RevId: 610006013

docs/build_mozc_in_docker.md

@@ -128,12 +128,11 @@ bazel test base:util_test --config oss_linux -c dbg
 ### Output logs to stderr
 
 ```
-bazel test base:util_test --config oss_linux --test_arg=--logtostderr --test_output=all
+bazel test base:util_test --config oss_linux --test_arg=--stderrthreshold=0 --test_output=all
 ```
 
-* The `--test_arg=--logtostderr --test_output=all` flags shows the output of
-unitests to stderr.
-
+*   The `--test_arg=--stderrthreshold=0 --test_output=all` flags shows the
+    output of unitests to stderr.
 
 ## Build Mozc on other Linux environment