Give core registry libraries public visibility

This is so Donuts can create entirely separate Bazel repositories that
link against the Domain Registry codebase.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=116182448

java/com/google/domain/registry/keyring/api/BUILD

@@ -6,6 +6,7 @@ package(
 java_library(
     name = "api",
     srcs = glob(["*.java"]),
+    visibility = ["//visibility:public"],
     deps = [
         "//java/com/google/common/base",
         "//third_party/java/bouncycastle",