buffer: do not always use defaults

The Buffer#(read|write)U?Int(B|L)E functions should not use a default
value. This is very likely a bug and it was never documented that
way.

Besides that this also improves the tests by adding more tests and by
refactoring them to less code lines.

PR-URL: https://github.com/nodejs/node/pull/20054


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Khaidi Chu <i@2333.moe>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>