Call init and finalization functions per extension message

Previously, init and finalization function for extensions are called
per extension block, rather than per message.  This commit changes
that behaviour, and now they are called per message.  The parse
function is still called per extension block.

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3244)