util: convert inspect.styles and inspect.colors to prototype-less objects

Use a prototype-less object for inspect.styles and inspect.colors to allow
modification of Object.prototype in the REPL.

Fixes: https://github.com/nodejs/node/issues/11614
PR-URL: https://github.com/nodejs/node/pull/11624


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>