util: improve inspect performance

This significantly improves the inspection performance for all array
types. From now on only the visible elements cause work instead of
having to process all array keys no matter how many entries are
visible.

This also moves some code out of the main function to reduce the
overall function complexity.

PR-URL: #22503
Reviewed-By: Matteo Collina <[email protected]>
Reviewed-By: John-David Dalton <[email protected]>
Reviewed-By: Benjamin Gruenbaum <[email protected]>
Reviewed-By: Refael Ackermann <[email protected]>