[roll third_party/pigweed] pw_protobuf_compiler: Handle deps on nanopb.proto

- Add a pw_proto_library for nanopb.proto to the CMake build.
- Skip recompiling nanopb.proto when running protoc for Nanopb.
- Add the pw_protobuf_compiler Nanopb test to CMake.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/46961

third_party/pigweed Rolled-Commits: e22ac20e5e7dc65..bcaf883773fc10a
Roller-URL: https://ci.chromium.org/b/8846155895944305440
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8846155895944305440
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Iabeae35b0702d6261e7627579b9fecdead65a10c
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/47086
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 e22ac20..bcaf883 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit e22ac20e5e7dc65a5ddf5b9397f6407957683de7
+Subproject commit bcaf883773fc10ac614b60593ab565b1a721e7fb