Moving the auth_provider APIs into the core binary to avoid a chicken and

Moving the auth_provider APIs into the core binary to avoid a chicken and
egg problem when loading the auth modules vs the providers.  (Can't load the
auth module until the provider has registered.  Can't register the provider until
the auth module is loaded and APIs are available.)

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@96846 13f79535-47bb-0310-9956-ffa450edef68