Without warning, INFRA broke several of our GitHub Actions workflows, and have been unresponsive all week. See https://issues.apache.org/jira/browse/INFRA-21239. Since then, the Rust developers have removed their offending actions, so those are no longer blocked. This PR does harm reduction for C++ and R workflows, moving the workflows that INFRA doesn't like to their own files (temporarily, I hope, while this business gets sorted out). This enables the other workflows in each file to run, so we at least get some C++ and R tests running, and we can still verify on our personal forks the workflows that have been blocked on apache/arrow.