Upgrade to golang protobuf api v2

Major operations:
 * Fix the go_package entries to be consistent, as the new tool
   complains when it doesn't have a '/'.
 * Regenerate with the new protoc-gen-go tool.
 * github.com/golang/protobuf -> google.golang.org/protobuf
 * proto.[Un]MarshalText -> prototext.[Un]Marshal

Change-Id: Ie1147bd2457fafb66ba555461b3bf14f0561a25d
diff --git a/cmd/extract_apks/bundle_proto/targeting.proto b/cmd/extract_apks/bundle_proto/targeting.proto
index cdc910b..a33edc7 100644
--- a/cmd/extract_apks/bundle_proto/targeting.proto
+++ b/cmd/extract_apks/bundle_proto/targeting.proto
@@ -6,7 +6,7 @@
 
 package android.bundle;
 
-option go_package = "android_bundle_proto";
+option go_package = "android/soong/cmd/extract_apks/bundle_proto";
 option java_package = "com.android.bundle";
 
 // Targeting on the level of variants.