lib: rename validateSafeInteger to validateInteger

validateInteger() was renamed to validateSafeInteger() in
https://github.com/nodejs/node/pull/26572. However, this
function also works with unsafe integers. This commit restores
the old name, and adds some basic tests.

PR-URL: https://github.com/nodejs/node/pull/29184
Refs: https://github.com/nodejs/node/pull/26572


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>