Revert "[base] Replace base::Optional with Abseil"

This reverts commit f2e25f8a.

Reason for revert: Breaks GCC 8.4.0 compilation, see bug.

Original change's description:
> [base] Replace base::Optional with Abseil
>
> Change base::Optional to an alias of absl::optional. Eventually we
> should remove it entirely.
>
> Bug: v8:11006
> Change-Id: I687d44cc7e7cd0a49a84bcc207231eb6808eef2d
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2476318
> Commit-Queue: Leszek Swirski <leszeks@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#76913}

Bug: v8:11006, v8:12252
Change-Id: I8048dee676a36551d15f25a31d1e171dae00d975
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3173672
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#76976}

BUILD.gn

@@ -4904,8 +4904,6 @@ v8_component("v8_libbase") {
 
   deps = [ ":v8_config_headers" ]
 
-  public_deps = [ ":v8_abseil" ]
-
   data = []
 
   data_deps = []

test/wasm-api-tests/BUILD.gn

@@ -9,7 +9,6 @@ v8_executable("wasm_api_tests") {
 
   deps = [
     "../:common_test_headers",
-    "../..:v8_abseil",
     "../..:v8_internal_headers",
     "../..:v8_maybe_icu",
     "../..:wee8",

tools/gcmole/BUILD.gn

@@ -26,7 +26,6 @@ group("v8_run_gcmole") {
     "../../test/cctest/",
     "../../test/common/",
     "../../testing/gtest/include/gtest/gtest_prod.h",
-    "../../third_party/abseil-cpp/",
     "../../third_party/googletest/src/googletest/include/gtest/gtest_prod.h",
     "../../third_party/icu/source/",
     "../../third_party/wasm-api/wasm.h",

tools/gcmole/gcmole.py

@@ -103,7 +103,6 @@ def MakeClangCommandLine(plugin, plugin_args, arch_cfg, clang_bin_dir,
       "-I./",
       "-Iinclude/",
       "-Iout/build/gen",
-      "-Ithird_party/abseil-cpp",
       "-Ithird_party/icu/source/common",
       "-Ithird_party/icu/source/i18n",
   ] + arch_cfg.arch_options)