pw_rpc: Raw method implementation

This change adds a new RPC method implementation which calls methods
with raw binary protobuf data. The structure largely follows that of
nanopb methods, with a similar API for generated code.

Change-Id: Ia3284f62a21b4c8c467109c9577b67bef1fc1cce
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/20120
Commit-Queue: Alexei Frolov <frolv@google.com>
Reviewed-by: Wyatt Hepler <hepler@google.com>
diff --git a/pw_rpc/BUILD.gn b/pw_rpc/BUILD.gn
index ef1884f..8c67797 100644
--- a/pw_rpc/BUILD.gn
+++ b/pw_rpc/BUILD.gn
@@ -166,7 +166,10 @@
     ":server_test",
     ":service_test",
   ]
-  group_deps = [ "nanopb:tests" ]
+  group_deps = [
+    "nanopb:tests",
+    "raw:tests",
+  ]
 }
 
 pw_proto_library("test_protos") {