Expand responsefile content in trace output

Desired Behavior

When using --trace-file, for very long command lines, show arguments passed to ocaml*.exe instead of -args0 responsefile.data.

When profiling Dune and in particular external commands called with -args0 / -args it's hard/impossible to tell what was actually passed to the external command. For example, for ocamlc executions you cannot always see what source file was actually compiled.

Example

I propose that instead of logging Args: -args0 responsefile.data instead it logs Args: <content of responsefile>, so

Args: <very long list of options> -c file.ml

Alternatively, another value is logged, ReponseFileContent or similiar, with the content of the file:

Args: -args0 responsefile.data
ResponseFileContent: <very long list of options> -c file.ml

Start from the --trace-file handling for external commands and the -args0/-args response-file path, using the ocamlc example as the reference case. Trace how Args output is produced, then verify that the trace exposes response-file contents or a separate response-file entry while preserving the command arguments.