feat(cli/test): deno test --clean

[iuioiua]

The result of the call is ignored as it throws even when the directory does not exist.

Closes #23491

[bartlomieju]

Please add an integration test

[lucacasonato]

This has the downside that you can not run multiple deno test calls in parallel, or even in series unless you specify a different directories.

[iuioiua]

I think it's a fair trade-off, as long as the behaviour is clearly documented. Perhaps, if we receive too many complaints, which we may not, we can add a --no-clean, or similar, flag.

For context, I recently waited for ~5 minutes on my M2 MacBook to delete /coverage for std.

[lucacasonato]

The point is, as is, this PR breaks existing workflows

[iuioiua]

We could make this behaviour opt-in via --clean-cov-dir (or similar) and then at some point decide whether we make this default behaviour in Deno 2.

[iuioiua]

I've changed my mind. I think this should just be opt-in for good.

[iuioiua]

Should this only work with --coverage?