Add BuildKite pipeline filegroup. Make platforms_bzl more widely visible.

PiperOrigin-RevId: 454040412

BUILD

@@ -63,6 +63,12 @@ yaml_test(
     schema = "@github_workflow_schema//file",
 )
 
+filegroup(
+    name = "buildkite_pipelines",
+    srcs = glob([".buildkite/*.yaml"]),
+    visibility = ["//:sandbox"],
+)
+
 yaml_test(
     name = "buildkite_pipelines_test",
     srcs = glob([".buildkite/*.yaml"]),

tools/bazeldefs/BUILD

@@ -8,7 +8,7 @@ package(
 bzl_library(
     name = "platforms_bzl",
     srcs = ["platforms.bzl"],
-    visibility = ["//visibility:private"],
+    visibility = ["//:sandbox"],
 )
 
 bzl_library(