Add go_package names to .proto files used by BEP.

This makes it possible to use these files as part of Buildbarn in
literal form. Some manual changes to BUILD.bazel files are still
necessary, but those should be unnecessary when Gazelle gains decent
support for dealing with multiple .proto files in one directory.

src/main/java/com/google/devtools/build/lib/buildeventstream/proto/build_event_stream.proto

@@ -16,6 +16,7 @@ syntax = "proto3";
 
 package build_event_stream;
 
+option go_package = "github.com/bazelbuild/bazel/src/main/java/com/google/devtools/build/lib/buildeventstream/proto";
 option java_package = "com.google.devtools.build.lib.buildeventstream";
 option java_outer_classname = "BuildEventStreamProtos";
 

src/main/protobuf/command_line.proto

@@ -15,6 +15,7 @@
 syntax = "proto3";
 package command_line;
 
+option go_package = "github.com/bazelbuild/bazel/src/main/protobuf";
 // option java_api_version = 2;
 option java_package = "com.google.devtools.build.lib.runtime.proto";
 

src/main/protobuf/invocation_policy.proto

@@ -15,6 +15,7 @@
 syntax = "proto2";
 package blaze.invocation_policy;
 
+option go_package = "github.com/bazelbuild/bazel/src/main/protobuf";
 // option java_api_version = 2;
 option java_package = "com.google.devtools.build.lib.runtime.proto";
 

src/main/protobuf/option_filters.proto

@@ -14,6 +14,7 @@
 syntax = "proto3";
 package options;
 
+option go_package = "github.com/bazelbuild/bazel/src/main/protobuf";
 // option java_api_version = 2;
 option java_package = "com.google.devtools.common.options.proto";