Leverage dependency injection for the Introspector object

Created by: drupol

There are many places in this library where Introspector::detect() and Introspector::parse() are used.

This prevent users to override that object. Especially in ecphp/eu-login-bundle where the Introspector should be customized in order to take in account custom CAS properties returned by EU Login.

The ultimate goal of this issue will be to provide an update of ecphp/eu-login-bundle where the Introspector would parse the EU Login response properly, without the need to copy paste a custom function in the EU Login User Provider.