[roll third_party/pigweed] docs: Add using-directive exception for literals

The Google external style guide forbids the usage of using-directives,
regardless of scope. In Pigweed, there are many using-directives for the
purposes of including literal operators, such as std::chrono_literals
and pw::bytes. This CL adds an explicit exception for such uses to the
rule for the Pigweed codebase.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/96901

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 5dccd362cb789ca..b359846605a7844
Roller-URL: https://ci.chromium.org/b/8811804937836883201
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8811804937836883201
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I44235f731c6cda36ec70965e4861cffce1704c63
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/97661
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 5dccd36..b359846 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 5dccd362cb789cac5f065668214361f031b6cf62
+Subproject commit b359846605a7844a9febbdc6c91b7c07cdb8eeb7