allow *%W for better readability (Lint/UnneededSplatExpansion)

[md-work]

In certain scenarios, using *%W may improve readability. So there should be exceptions to: Lint/UnneededSplatExpansion

Most of those scenarios are when building shell commands.

E.g.:

# filename may be an arbitrary string, containing spaces and other weird stuff.
filename = "file \" ' name.txt"

# Unsafe!
# May lead to wrong behavior. E.g. delete `file` and `name.txt`, but not `file name.txt`.
system('sudo -u ' + target_user + '/usr/bin/rm -r -- ' + filename)
system("sudo -u '#{target_user}' -- /usr/bin/rm -r -- '#{filename}'")

# Safe, but hard to read.
# And this rm example is still a simple shell command.
# Longer shell commands get much harder to read in this style.
system('sudo', '-u', target_user, '/usr/bin/rm', '-r', '--', filename)

# Safe and good to read. But triggers Lint/UnneededSplatExpansion
# *%W[ isn't very pretty to read. But the important shell command is clearly recognizable
system(*%W[sudo -u #{target_user} -- /usr/bin/rm -r -- #{filename}])

Be aware, that system is not the only method covered by this. Open3.... is also affected and I'm actually using a custom method with adds additional checks when running external command. So excluding Lint/UnneededSplatExpansion for certain methods may not be a satisfying solution.

This is similar to #3512
But here the problem is, that using *%W explicitly improves readability.

[md-work]

Moved to: rubocop/rubocop#7041