[roll third_party/pigweed] pw_transfer: Initial C++ service

This starts the RPC transfer service in C++. Initially, only simple read
transfers are supported, where all read data is sent synchronously in
response to parameter requests from the client.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/53140

third_party/pigweed Rolled-Commits: b2489f336ee2945..f93cb26beee3f0e
Roller-URL: https://ci.chromium.org/b/8840261890572072640
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8840261890572072640
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Iffcd8374305bee4f4dcb0a14fc039a412e519276
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/55263
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 b2489f3..f93cb26 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit b2489f336ee2945e3f932e4d8d827bc6af9ebbdb
+Subproject commit f93cb26beee3f0eb38603407a24e4451acf536a7