`rules_java` seem to not work with `--nolegacy_external_runfiles` flag

The flag docs state:
```# Do not build runfiles symlink forests for external repositories under
# `.runfiles/wsname/external/repo` (in addition to `.runfiles/repo`). This reduces runfiles &
# sandbox creation times & prevents accidentally depending on this feature which may flip to off by
# default in the future. Note, some rules may fail under this flag, please file issues with the rule
# author.
# Docs: https://bazel.build/reference/command-line-reference#flag--legacy_external_runfiles
```

If the flag is added to `.bazelrc`, tests fail with java not found:
```
/private/var/tmp/_bazel_Dan/30d3419be7d4a27db6dff5dc2d690288/sandbox/darwin-sandbox/5542/execroot/_main/bazel-out/darwin_x86_64-fastbuild/bin/plugin-bazel/src/plugin_tests.runfiles/_main/plugin-bazel/src/plugin_tests: line 409: /private/var/tmp/_bazel_Dan/30d3419be7d4a27db6dff5dc2d690288/sandbox/darwin-sandbox/5542/execroot/_main/bazel-out/darwin_x86_64-fastbuild/bin/plugin-bazel/src/plugin_tests.runfiles/_main/external/rules_java~~toolchains~local_jdk/bin/java: No such file or directory
```

--nolegacy_external_runfiles を .bazelrc に追加し、影響を受けるプラグインテストを実行して失敗を再現します。まず、409 行付近にある生成済みの plugin_tests.runfiles スクリプトと、rules_java のローカル JDK パスを確認します。フラグを有効にした状態で Java テストが java を見つけてパスすれば完了です。

索引モデルが issue の本文から書いたものです。