[roll third_party/pigweed] pw_rpc: Java client visibility updates

- RpcKey must be public since it's part of the public API.
- Add a toString() to RpcKey that is similar to PendingRpc.
- Make MethodClient.method() public since there's no need for it to be
  private.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/126450

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: c0531c8375f1125..a9e1b4b76669c9a
Roller-URL: https://ci.chromium.org/b/8792239937216896769
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ie35bc5fee967926764abd23035d313c39fbd50fd
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/126422
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 c0531c8..a9e1b4b 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit c0531c8375f11255b31a6a58b51785f6501adbd6
+Subproject commit a9e1b4b76669c9ad65532bbea8a022134e28c3a5