Adds an Open function for the class abstraction that does nothing for
now.
This is a backport of [[https://github.com/bitcoin/bitcoin/pull/19334 | core#19334]] [3/4]
https://github.com/bitcoin/bitcoin/pull/19334/commits/2179dbcbcd0b9bef7ad9c907b85294b9a1bccf0f
Depends on D10023