QUIC APL: Defer default XSO creation

QUIC APL: Defer default XSO creation

QUIC in single-stream mode could be used with a protocol where the
server writes first or the client writes first. This determines
whether the single stream would be client or server initiated,
which affects the stream ID allocated to the stream. We should support
both client-sends-first and server-sends-first application protocols.
Thus, defer default XSO creation until the point in time at which
we know whether a client-first or server-first application protocol
is being used. We do this by taking whether SSL_read() or SSL_write()
is called first as a cue.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/20765)