[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/lecturio.py

@@ -22,14 +22,7 @@ class LecturioBaseIE(InfoExtractor):
     _LOGIN_URL = 'https://app.lecturio.com/en/login'
     _NETRC_MACHINE = 'lecturio'
 
-    def _real_initialize(self):
-        self._login()
-
-    def _login(self):
-        username, password = self._get_login_info()
-        if username is None:
-            return
-
+    def _perform_login(self, username, password):
         # Sets some cookies
         _, urlh = self._download_webpage_handle(
             self._LOGIN_URL, None, 'Downloading login popup')