Summary of Changes

I'm going to be blunt here. Our LDAP client class, lightweight and functional as it may be, is a piece of Joomla software that falls under the "abandonware but lucky the damn thing still works" category and its only actual use in core is for its bind and search capabilities (as in the write portion of the API is unused in core). This is one class that I'd personally argue in favor of throwing away and replacing with something that is getting more scrutiny and maintenance because the use of LDAP is a more exotic use case than normal and we just don't have the resources to keep up with it (ask the folks on JSST how difficult it was to ensure the escaping fixes we did actually worked). So, I'm basically throwing our LdapClient class away and pulling in Symfony's LDAP component as a replacement.

Why? Symfony's component does a lot of things better than we do; options validation, error reporting/handling, and abstracting data arrays into a developer friendly structure being three focus points.

Accepting this PR actually introduces two Symfony components into our application; the LDAP component, and the OptionsResolver; this second one is actually the one I find more interesting for general use because it gives you a way to pretty sanely validate arrays and enforce things like key presence, default key values, and throwing errors on missing required keys (joomla-framework/database#101 is an example of validating the database API's options array against the resolver).

Testing Instructions

LDAP Authentication continues to work as before

Documentation Changes Required

Nothing at this time