[roll third_party/pigweed] pw_rpc: Channel, Service, and Method Client

Add logic to support easily finding and invoking RPC methods in the
client library. In the future these objects could have class fields for
each service/method to enable greater discoverability.

The MethodStub is used to invoke RPC calls. It is equivalent to the
MethodClient in the python RPC library.

Original-Bug: b/194329554
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/60921

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 5be54582d9e51e7..1a53e514f835630
Roller-URL: https://ci.chromium.org/b/8835806339999618305
Cq-Cl-Tag: roller-builder:pigweed-sample-project-roller
Cq-Cl-Tag: roller-bid:8835806339999618305
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I671150f7e51d6cb350cc36fa67843cd8eb69d1ad
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/sample_project/+/61400
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 5be5458..1a53e51 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 5be54582d9e51e79b81ca31e006ff579f27242f1
+Subproject commit 1a53e514f83563006de355338563ca879dcef4ac