[DependencyInjection] Add a method map to avoid computing method names from service names

/cc @schmittjoh @stof

The diff is a bit messy because of indenting, but all this adds really is an `if(isset($this->methodMap[$id])) { $method = $this->methodMap[$id]; }` that bypasses the method_exists + strtr calls. It's not a huge improvements but saves some cycles on something that's typically called a few hundred times per request.