Report usages of Composer\Autoload\ClassLoader::findFileWithExtension as easily optimizable

[stof]

According to screenshots in https://qafoolabs.com/profiler/blog/analyzing-xhprof-traces and what I can see in this repo, you report the number of calls to Composer\Autoload\ClassLoader::findFile as being non-easily optimizable, which is true.
However, it would be great to report calls to Composer\Autoload\ClassLoader::findFileWithExtension as well, which is easily optimizable. When using an optimized Composer autoloader, it will never be called (except if you register some namespaces dynamically as these won't be optimized by Composer), while they will be called a lot by findFile otherwise (accounting for 80% of the time of findFile in this case)

[beberlei]

@stof Thanks for the hint. We have the optimized autoloader metric on our todo list as well so this will play well with it.