src: use `internalBinding('config').hasInspector` in JS land

Instead of `process.config.variables.v8_enable_inspector`
which depends on the variable name in gyp files, or detecting
`internalBinding('inspector').Connection`.

PR-URL: https://github.com/nodejs/node/pull/25291


Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>