[roll third_party/pigweed] pw_base64: Doxygenify the Encode() functions

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/156532

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 4e8d69fcbdf32b2..6f6d32dbb0b8013
Roller-URL: https://ci.chromium.org/b/8773756832235074081
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I589b5cc825fb632821e28a1449e097424a3d5ad1
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/162836
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 4e8d69f..6f6d32d 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 4e8d69fcbdf32b245294f4a58e39dc99653a51b7
+Subproject commit 6f6d32dbb0b8013e9e4a16de06003f90fdbfde5d