Materialize important outputs from remote external repos

[fmeum]

Important outputs and runfiles from external repos that are remote repo contents cache hits got stuck at various levels of the materialization pipeline for being source artifacts. This is fixed by consolidating the skip logic in a RemoteOutputChecker static helper.

[fmeum]

@bazel-io fork 9.0.0

[gemini-code-assist]

Code Review

The pull request effectively addresses the issue of runfiles from remote external repositories not being materialized correctly by consolidating the skip logic into a new RemoteOutputChecker.mayBeRemote static helper. This change improves code maintainability by centralizing the logic for determining if an ActionInput could be remote. Additionally, the ActionExecutionMetadata parameter in ActionInputPrefetcher.prefetchFiles has been made nullable, which correctly handles scenarios where a generating action might not be available. The new testRun test case provides good coverage for the bazel run command's interaction with the remote repository contents cache, ensuring the fix works as expected.