There is no constructor code when creating an inspector `Session`
instance in Node. Also get rid of some symbols which should've been
private properties. This PR doesn't yet add any new implementations
though as these are mostly cosmetic changes.
For some reason we didn't register the `node:inspector` module, which
lead to a panic when trying to import it. This PR registers it.
Related: https://github.com/denoland/deno/issues/25004
