[base] Add base::expected

This change introduces base::expected, a C++17 backport of C++23's
std::expected. Similarly to other STL backports in Chromium, this
port tries to replace UB with deterministic program termination where
possible, and does not support exceptions.

base::expected<T, E> can be thought of as a variant of the value type
`T` and error type `E`, with an API similar to absl::optional<T>.

Prior Art:
* llvm::Expected: https://llvm.org/doxygen/classllvm_1_1Expected.html
* WTF::Expected:
    https://github.com/WebKit/webkit/blob/main/Source/WTF/wtf/Expected.h
* tl::expected: https://github.com/TartanLlama/expected
* Rust's std::result::Result:
    https://doc.rust-lang.org/stable/std/result/enum.Result.html

References:
* Proposal: https://wg21.link/P0323
* C++ Draft: https://eel.is/c++draft/expected
* C++ Ref: https://en.cppreference.com/w/cpp/header/expected

Change-Id: I1e18de1fbec5e621805c90f1b49324db128a4681
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3453963
Reviewed-by: Giovanni Ortuno Urquidi <ortuno@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Commit-Queue: Jan Wilken Dörrie <jdoerrie@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1002594}

base/BUILD.gn

@@ -918,6 +918,8 @@ mixed_component("base") {
     "trace_event/trace_id_helper.h",
     "traits_bag.h",
     "tuple.h",
+    "types/expected.h",
+    "types/expected_internal.h",
     "types/id_type.h",
     "types/pass_key.h",
     "types/strong_alias.h",
@@ -3307,6 +3309,7 @@ test("base_unittests") {
     "tools_sanity_unittest.cc",
     "traits_bag_unittest.cc",
     "tuple_unittest.cc",
+    "types/expected_unittest.cc",
     "types/id_type_unittest.cc",
     "types/pass_key_unittest.cc",
     "types/strong_alias_unittest.cc",