Logstash pipeline systax errors after 7.6.0

In 7.6.0, changes were introduced to add source-file metadata to nodes (elastic/logstash#11456), which was intended to provide greater visibility when debugging pipelines that were composed of many source files. An untended consequence of this is that by parsing the files individually instead of pre-concatenating them, we no longer could parse configurations whose individual files weren't syntactically complete (elastic/logstash#11598). Work is ongoing to find a solution that gets us this source-file metadata in a manner that restores in-the-wild composition styles.