Implement faster FilteredRecursiveDirectoryIterator

[staabm]

closes #135

running parallel lint in https://github.com/FriendsOfREDAXO/rexstan with vendor/bin/parallel-lint . --exclude vendor takes 0.3 seconds with this PR while it took 9 seconds before the PR

[staabm]

@jrfnl anything I can do to move this forward?

[jrfnl]

@staabm Not really. I'll try to find some time to review this over the next few weeks. That should hopefully help, but this is, in my experience, generally speaking a slow moving repo, so patience is the keyword...

[staabm]

Tbh I have implemented against 1.x - we need to verify it against 2.x (and see whether the speed improvements are still visible on 2.x)

[staabm]

let my clarify my last comment: the PR works in parallel-lint 1.x which I am currently using and it gives a decent speed boost, because without it, vendor files get linted even though I am passing --exclude vendor.

I did not verify the fix on parallel-int 2.x .. it looks like on 2.x the vendor is properly ignored even before this patch

[staabm]

@jrfnl we just talked about this :-)

(It might no longer be relevant)

[staabm]

I can no longer reproduce the slownes in the latest 1.4.x release