Add a check if "which" command exist

Is your feature request related to a problem? Please describe.
Some minimal system configurations present on Arch Linux doesn't install "which" by default and advertises it as a separate package to install manually.

Describe the solution you'd like
Add a check for which command existing and abort the script if it is not found.

Describe alternatives you've considered
Ask package maintainers to require the which program to be installed.

[luebking]

The canonical answer is that "which" should not be used for this anyway.
https://gitlab.archlinux.org/archlinux/packaging/packages/visualvm/-/work_items/2#note_446492
https://mywiki.wooledge.org/BashFAQ/081

Should be this edited or reopened in favor of the new one?

[luebking]

This issue wasn't closed but the correct™ fix for the problem from virtualvm's side is to simply not use "which" in any scripts, not to handle its absence.

[thurka]

I will take a look, but platform/lib/nbexec is not part of VisualVM sources. It comes from netbeans platform.

[thurka]

Done in master.