* Added config `runnables.extraTestBinaryArgs` to control the args.
* The default is `--show-output` rather than `--nocapture` to prevent
unreadable output when 2 or more tests fail or print output at once.
* Renamed variables in `CargoTargetSpec::runnable_args()` for clarity.
Fixes <https://github.com/rust-lang/rust-analyzer/issues/12737>.