[roll third_party/pigweed] pw_protobuf: FieldKey class

This replaces the MakeKey function with a FieldKey class, which can be
used to both create and parse a protobuf field key.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/59641

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: ddfc077efac67c3..5ebf8add166d5ba
Roller-URL: https://ci.chromium.org/b/8836427955552632113
Cq-Cl-Tag: roller-builder:pigweed-sample-project-roller
Cq-Cl-Tag: roller-bid:8836427955552632113
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ia930fe44d467fa4dfb0dbc6c7692d47294d484b1
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/sample_project/+/60540
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 ddfc077..5ebf8ad 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit ddfc077efac67c34b3222b9dfc48f504c477ec0b
+Subproject commit 5ebf8add166d5ba4eecb4617069e9e531c84c016