Auto merge of #38185 - jsgf:test-list, r=alexcrichton

Auto merge of #38185 - jsgf:test-list, r=alexcrichton

libtest: add --list option to list tests and benchmarks

This option lists all the tests and benchmarks a binary provides without running any of them.
By default the listing is sent to stdout (intended for human consumption), but if `--logfile` is also specified, it is also written there in an easily parsable form.

If filters are specified, they're applied before the output is emitted. The human output will also include a summary unless `-q` is specified.