[roll third_party/pigweed] pw_tokenizer: Rework pw_tokenizer.detokenize.PrefixedMessageDecoder

- Rename PrefixedMessageDecoder to NestedMessageDecoder. This class will
  be expanded and made specific to nested tokenized messages.
- Support detokenizing from byte strings in addition to files in
  PrefixedMessageDecoder. Partial messages are preserved between calls.
- Expand unit tests.
- Pull the detokenize module into the API reference docs.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/167150

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 3469faa09655ed2..96a96793700ac12
Roller-URL: https://ci.chromium.org/b/8772017899096788657
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I11558cbc3f96de60b992c15594568869fc702f18
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/167867
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 3469faa..96a9679 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 3469faa09655ed28857849c06d9f78245497d360
+Subproject commit 96a96793700ac123587880569a06304d3a9fe463