make @std/path cross-runtime

**Is your feature request related to a problem? Please describe.**

I'm looking for a good isomorphic path library in javascript that can be used in both the browser and Node. I can't move to Deno just yet, but `@std/path` looks great!

From https://github.com/denoland/std/issues/4914 it seems like it may already be cross-platform, or at least close to it. However it's not [marked as such on jsr](https://jsr.io/@std/path).

**Describe the solution you'd like**

If it's indeed cross platform, update the jsr page. If not, what are the gotchas? can a subset of it be safely used? Is there a way I can check myself other than trying to use it and hoping I bump into incompatibility errors before they cause actual bugs?