_perform_login
* Adds new functions `_initialize_pre_login` and `_perform_login` as part of the extractor API * Adds `ie.supports_login` to the public API
Based on https://github.com/ytdl-org/youtube-dl/pull/25922 Closes #2710, https://github.com/ytdl-org/youtube-dl/issues/5856 Authored by: pycabbage, Lesmiscore