[roll third_party/pigweed] pw_rpc: Add ClientServer combination

This adds a class which wraps both an RPC client and server, simplifying
setup and usage in systems that require both.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/40624

third_party/pigweed Rolled-Commits: 4ea2de8fa56cd6f..3e28092cd59477c
Roller-URL: https://ci.chromium.org/b/8850019948802252320
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8850019948802252320
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I07ea2327aa65e0c27c7ce1877225a7636668f8fc
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/40862
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 4ea2de8..3e28092 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 4ea2de8fa56cd6fc5e622a229c4d94d77bcc2fe9
+Subproject commit 3e28092cd59477cf09727d6e6357cc993d565f9b