Add new Atomic File Operations rule

[ydah]

Follow: rubocop/rubocop#10696

When doing file operations after confirming the existence check of a file, frequent parallel file operations may cause problems that are difficult to reproduce.
Therefore, it is preferable to use atomic file operations.

# bad - race condition with another process may result in an error in `mkdir`
unless Dir.exist?(path)
  FileUtils.mkdir(path)
end

# good - atomic and idempotent creation
FileUtils.mkdir_p(path)

# bad - race condition with another process may result in an error in `remove`
if File.exist?(path)
  FileUtils.remove(path)
end

# good - atomic and idempotent removal
FileUtils.rm_f(path)

[pirj]

Thank you!

[pirj]

It may be understood that those two snippets belong to a single example, while those are two separate ones and put corresponding good examples closer to bad ones.

WDYT of:

# bad - race condition with another process may result in an error in `mkdir`
unless Dir.exist?(path)
  FileUtils.mkdir(path)
end

# good - atomic and idempotent creation
FileUtils.mkdir_p(path)

# bad - race condition with another process may result in an error in `remove`
if File.exist?(path)
  FileUtils.remove(path)
end

# good - atomic and idempotent removal
FileUtils.rm_f(path)

The above addresses two problems:

1. Confusion with what the example is
2. Order of good and bad

Leaving the order (bad, bad, good, good vs bad, good, bad, good) up to you. I found one example of the second kind of ordering, but pretty sure one could find examples of bad, bad, good, good, too. So it's subjective and I leave it to your judgement how you want to do it.

[ydah]

I was conforming to the nearby good/bad case style, but it may indeed be confusing in a case like this.
I thought the bad, good, bad, good order you gave as an example looked good and I'll rewrite it. Thank you so much.

[tdeo]

I indeed like the explanation of what concurrency issue can arise, maybe even specify the errors that could happen: already exists for mkdir and does not exist for remove?