ssl: move OpenSSL library initialization code to separate file

We redefine ssl_init and ssl_free in the EE build, because we need to do
some extra work there. Currently, it's fine to duplicate the bulk of the
OpenSSL library initialization code between EE and CE repositories, but
with the introduction of OpenSSL 3.0 it's going to become more
complicated so duplicating would look bad. Let's move the common code to
ssl_init_impl() and ssl_free_impl() helper functions.

Needed for #6477

NO_DOC=refactoring
NO_TEST=refactoring
NO_CHANGELOG=refactoring

(cherry picked from commit f9739160)