Empty FUNCTION statement detected should be allowed for around plugins

[markshust]

Description

A WARNING is thrown for sniff "Empty FUNCTION statement detected"

This warning should not be through if the empty function is an around plugin. A common use-case for around plugins is to prevent execution of the original calling method. For example:

    public function aroundPrepareFavicon(Renderer $subject, callable $proceed)
    {
        // Do not call $proceed() to remove favicon code
    }

Expected behavior

I would expect this sniff to still run and throw a WARNING in all circumstances other than an around plugin. The sniff should not throw a WARNING for an around plugin.

A consideration may be to mandate the use of a comment for an around plugin with an empty function statement. This would ensure that the empty around plugin not calling the callable $proceed is desired. See above for an example comment which explains why this around plugin is empty.

Benefits

Empty around plugins are not only valid but this is a common use-case. The sniff should not detect this as an error. A comment within an empty around plugin would also most likely be desired and document to the user why this around function is empty.

[lenaorobei]

#126