[roll third_party/pigweed] pw_tokenizer: Move Base64 functions to class

- Move the Base64 tokenization functions to the tokenizer class, which
  is much cleaner to work with.
- Have AutoUpdatingDetokenizer derive from Detokenizer. This makes
  working with detokenizers simpler.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/47761

third_party/pigweed Rolled-Commits: b2062fd8d667a6f..5f53d27f84e1519
Roller-URL: https://ci.chromium.org/b/8845319737727438832
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8845319737727438832
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ibd2d8dac9f51aac481ca1d0e800c090972435398
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/47920
Reviewed-by: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index b2062fd..5f53d27 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit b2062fd8d667a6f46462adb28d6b13847d271cb2
+Subproject commit 5f53d27f84e151969015f7fa91b5516c3e8582e8