Bug #63252 for Perl-Critic: Faster rewrite of Variables::ProhibitReusedNames

After some profiling, I found that Variables::ProhibitReusedNames was approximately 30% of the perlcritic runtime on some of our largest files. I was going to just disable it when I read this comment in the POD: "The current implementation walks the tree over and over. For a big file, this can be a huge time sink. I'm considering rewriting to search the document just once for variable declarations and cache the tree walking on that single analysis." So I decided to give rewriting it a try. Rather than caching, I've altered the policy to apply to the document as a whole and then recursively descend, bubbling up all the errors that it encounters. I was a little worried that the recursion might bloat memory for a second but the PPI objects dwarf the recursion overhead on any decent size document (which is what I was aiming to optimize anyway). I have an 8000 line perl module that takes about 18 seconds to process using the official ProhibitReusedNames and only 9 seconds with the attached version. That's not as fast as I was hoping for but its certainly a huge improvement (which can probably be improved even further). Also, in case anyone is worried, it still runs a tiny bit faster on just a few line document (0.696s vs 0.709s on my box, fwiw) The attached code (I didn't bother with a patch, since I rewrote everything from 'applies_to' down) also passes the regression tests perfectly (although those don't really exercise the possibility of false positives). More importantly for me, I get the same results on all the multi-thousand line modules I could find to test it on (written by people whose code I don't generally trust, since they wrote multi-thousand line modules). I was also a little worried that this wouldn't be 'acceptable' P::C style since it 'applies_to' the entire document and then searches for its specific violations but CodeLayout::RequireConsistentNewlines does the same thing so I felt vaguely justified. Let me know what you think.