roll: third_party/pigweed pw_rpc2: Add method metadata and update payload serialization

- Add MethodType and MethodInfoTag to describe RPC methods for generated
  code.
- Move serialize.h and pwpb_serialize.h to pw::rpc2::internal.
- Update pwpb_serialize to statically check that a message struct
  matches its message table and move sizing/encoding helpers out-of-line
  into pwpb_serialize.cc.
- Remove unused DeserializeInto and Deserialize(ConstBuf&&) helpers from
  serialize.h and pwpb_serialize.h.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/484390
Original-Revision: e6a63b7d4ebd25cd2d890097113d41889bf6c237

Rolled-Repo: https://pigweed.googlesource.com/pigweed/pigweed
Rolled-Commits: 13fe9248aaac88..e6a63b7d4ebd25
Roll-Count: 1
Roller-URL: https://cr-buildbucket.appspot.com/build/8669360787787543409
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I8c643c8b687a6f861ff6d1301b3d4544f3b9a9ae
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/488869
diff --git a/third_party/pigweed b/third_party/pigweed
index 13fe924..e6a63b7 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 13fe9248aaac886df98ced485a084ede7b4ed159
+Subproject commit e6a63b7d4ebd25cd2d890097113d41889bf6c237