[roll third_party/pigweed] pw_protobuf: Support WriteBytes from Reader

Adds a new variant of WriteBytes method in StreamEncoder that takes
payload from a stream::Reader. This can be useful for scenarios where
payload comes from non-in-memory sources such as storage. A
use case is UpdateBundle in pw_software_update, which needs to
construct a proto-format manifest from metadata on storage.

Original-Bug: 456
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/59481

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 217ef79f0f88f9b..5d15dbe0d5c6a00
Roller-URL: https://ci.chromium.org/b/8837035758850897521
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8837035758850897521
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I9ba545b0ea37746f9e06600703dd7ef82969a4bb
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/59861
Bot-Commit: 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 217ef79..5d15dbe 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 217ef79f0f88f9b56dca7a61d3fa19a6f50f67d5
+Subproject commit 5d15dbe0d5c6a0082861c47fb70a08392d1f6bef