pw_build: Switch to pw_* target types

This change replaces the implicit overrides of the default GN target
types in BUILDCONFIG.gn with explicit pw_* versions. This is done to
allow Pigweed to build within larger GN projects without modifying their
BUILDCONFIG files.

Change-Id: I1d1e41d5e9bde8fe076f7031f3c2b98b9630ff70
diff --git a/pw_rpc/BUILD.gn b/pw_rpc/BUILD.gn
index 2a6b637..404429c 100644
--- a/pw_rpc/BUILD.gn
+++ b/pw_rpc/BUILD.gn
@@ -12,6 +12,7 @@
 # License for the specific language governing permissions and limitations under
 # the License.
 
+import("$dir_pw_build/target_types.gni")
 import("$dir_pw_docgen/docs.gni")
 import("$dir_pw_protobuf_compiler/proto.gni")
 import("$dir_pw_unit_test/test.gni")
@@ -34,7 +35,7 @@
          "_pw_rpc_server_library requires an implementation to be set")
   _target_name = target_name
 
-  source_set(_target_name) {
+  pw_source_set(_target_name) {
     forward_variables_from(invoker, "*")
 
     public_configs = [ ":default_config" ]
@@ -78,7 +79,7 @@
 }
 
 # Classes with no dependencies on the protobuf library for method invocations.
-source_set("common") {
+pw_source_set("common") {
   public_configs = [ ":default_config" ]
   public_deps = [
     ":protos_pwpb",