I ended up changing the file system implementation to determine
its root directory as the last step of building it instead of being the
first step which makes it much more reliable.
This will respect `"type": "commonjs"` in a package.json to determine if
`.js`/`.jsx`/`.ts`/.tsx` files are CJS or ESM. If the file is found to
be ESM it will be loaded as ESM though.
Allows writing named sub-tests. These are:
1. Filterable on the command line via `cargo test ...`
2. Run in parallel
3. Use a fresh temp and deno dir for each test (unlike steps)
