Enable Starlark java_test in Bazel

This makes `--legacy_bazel_java_test` a no-op:   bazelbuild#17758

RELNOTES[INC]: --legacy_bazel_java_test is now a no-op

PiperOrigin-RevId: 516540643
Change-Id: If37fac1f6dab1659975c3a17fc3151e365a72b65

Author: hvadehra

src/main/starlark/builtins_bzl/bazel/exports.bzl

@@ -40,7 +40,7 @@ exported_rules = {
     "java_proto_library": java_proto_library,
     "+cc_proto_library": cc_proto_library,
     "+java_binary": java_binary,
-    "-java_test": java_test,
+    "+java_test": java_test,
     "py_binary": py_binary,
     "py_test": py_test,
     "py_library": py_library,