util: improve util.inspect performance

Fixes #14487 (closed)

A hole in a sparse array is now in itself a O(1) operation instead of O(n) where n is the number of coherent elements of the hole.

In addition a hasOwnProperty check was replaced with a cheaper one.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

util