[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/bilibili.py

@@ -821,11 +821,7 @@ class BiliIntlBaseIE(InfoExtractor):
             'extractor_key': BiliIntlIE.ie_key(),
         }
 
-    def _login(self):
-        username, password = self._get_login_info()
-        if username is None:
-            return
-
+    def _perform_login(self, username, password):
         try:
             from Cryptodome.PublicKey import RSA
             from Cryptodome.Cipher import PKCS1_v1_5
@@ -856,9 +852,6 @@ class BiliIntlBaseIE(InfoExtractor):
             else:
                 raise ExtractorError('Unable to log in')
 
-    def _real_initialize(self):
-        self._login()
-
 
 class BiliIntlIE(BiliIntlBaseIE):
     _VALID_URL = r'https?://(?:www\.)?bili(?:bili\.tv|intl\.com)/(?:[a-z]{2}/)?play/(?P<season_id>\d+)/(?P<id>\d+)'