lib: add static identifier codes for all deprecations

Assigns a static identifier code to all runtime and documentation
only deprecations. The identifier code is included in the emitted
DeprecationWarning.

Also adds a deprecations.md to the API docs to provide a central
location where deprecation codes can be referenced and explained.

PR-URL: https://github.com/nodejs/node/pull/10116


Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Michal Zasso <targos@protonmail.com>
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>