Allow Abseil's 128-bit integers in Chromium

Moves the status of absl::(u)int128 in Chromium from TBD to allowed.
Discussion: https://groups.google.com/a/chromium.org/g/cxx/c/6l8MlO7vEek

Change-Id: I1a64a5d4282e6988fd122bcb2da3aa665593ba94
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3405496
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Alex Turner <alexmt@chromium.org>
Cr-Commit-Position: refs/heads/main@{#963150}

styleguide/c++/c++-features.md

@@ -1576,6 +1576,24 @@ None
 
 The following Abseil library features are allowed in the Chromium codebase.
 
+### 128bit integer <sup>[allowed]</sup>
+
+```c++
+uint64_t a;
+absl::uint128 v = a;
+```
+
+**Description:** Signed and unsigned 128-bit integer types meant to mimic
+intrinsic types as closely as possible.
+
+**Documentation:**
+[Numerics](https://abseil.io/docs/cpp/guides/numeric)
+
+**Notes:**
+*** promo
+[Discussion thread](https://groups.google.com/a/chromium.org/g/cxx/c/6l8MlO7vEek)
+***
+
 ### Optional <sup>[allowed]</sup>
 
 ```c++
@@ -1714,24 +1732,6 @@ The following Abseil library features are not allowed in the Chromium codebase.
 See the top of this page on how to propose moving a feature from this list into
 the allowed or banned sections.
 
-### 128bit integer <sup>[tbd]</sup>
-
-```c++
-uint64_t a;
-absl::uint128 v = a;
-```
-
-**Description:** Signed and unsigned 128-bit integer types meant to mimic
-intrinsic types as closely as possible.
-
-**Documentation:**
-[Numerics](https://abseil.io/docs/cpp/guides/numeric)
-
-**Notes:**
-*** promo
-None
-***
-
 ### bind_front <sup>[tbd]</sup>
 
 ```c++