[roll third_party/pigweed] pw_rpc: Clean up comments; call MarkClosed() in MoveFrom()

- Have Call::MoveFrom() call MarkClosed() to reduce duplication.
- Set the call ID to 0 when a call is closed.
- Make the public set_on_next() function protected.
- Expand or update a few comments.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/126750

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: de048d847fb53ca..35c0f029b35ab92
Roller-URL: https://ci.chromium.org/b/8791511967433447953
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I243a5af7313ba407285c8f10e6c568e584acddbc
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/126744
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 de048d8..35c0f02 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit de048d847fb53cae433c092a8c59ff8a2e6f8190
+Subproject commit 35c0f029b35ab92e13d79bbca87e2f26acc2c4ed