Make java_stub_template.txt visible to @bazel_tools

Once this is released, `@bazel_tools` can re-export this publicly to preserve the old behavior. This is just temporary to avoid breaking any users for now. The plan is to drop this in the next major version bump.

PiperOrigin-RevId: 719206974
Change-Id: Ic99680e46507530f1c485429c291db934b3084f2

Author: hvadehra

java/bazel/rules/BUILD.bazel

@@ -44,3 +44,9 @@ filegroup(
     ],
     visibility = ["//java:__pkg__"],
 )
+
+# TODO: remove this in the next major version (rules_java 9.x / Bazel 9.x)
+exports_files(
+    ["java_stub_template.txt"],
+    visibility = ["@bazel_tools//tools/java:__pkg__"],
+)