[extractor] Add _perform_login function (#2943)

* Adds new functions `_initialize_pre_login` and `_perform_login` as part of the extractor API
* Adds `ie.supports_login` to the public API

yt_dlp/extractor/iqiyi.py

@@ -241,9 +241,6 @@ class IqiyiIE(InfoExtractor):
         '18': 7,    # 1080p
     }
 
-    def _real_initialize(self):
-        self._login()
-
     @staticmethod
     def _rsa_fun(data):
         # public key extracted from http://static.iqiyi.com/js/qiyiV2/20160129180840/jobs/i18n/i18nIndex.js
@@ -252,12 +249,7 @@ class IqiyiIE(InfoExtractor):
 
         return ohdave_rsa_encrypt(data, e, N)
 
-    def _login(self):
-        username, password = self._get_login_info()
-
-        # No authentication to be performed
-        if not username:
-            return True
+    def _perform_login(self, username, password):
 
         data = self._download_json(
             'http://kylin.iqiyi.com/get_token', None,