doc: fix structure and formatting in inspector.md

1. Reorder some sections alphabetically.
2. Fix some heading levels.
3. Express a type of a property more formally.

PR-URL: https://github.com/nodejs/node/pull/21709


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Claudio Rodriguez <cjrodr@yahoo.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>