refactor: Make GetWarnings() bilingual_str aware internally
https://github.com/bitcoin/bitcoin/pull/19233/commits/38e33aa481cefbe12c50f344bae190c0d95fb489
Make GetWarnings() return bilingual_str
https://github.com/bitcoin/bitcoin/pull/19233/commits/d1ae7c0355662481a7d181a0a458284936d53eb1
Make SetMiscWarning() accept bilingual_str argument
https://github.com/bitcoin/bitcoin/pull/19233/commits/d49612f98add29066817b7c808b76c2d728948e5
This is a backport of core#19233