Move Http2Optional to QuicheOptional.
This is part of the overall effort to merge quic, spdy, and http2 platform in
QUICHE.
gfe-relnote: n/a, no functional change.
PiperOrigin-RevId: 289853288
Change-Id: I98711f5dd54db265c29f337a73ad71c5400b227c
QUICHE (QUIC, Http/2, Etc) is Google‘s implementation of QUIC and related protocols. It powers Chromium as well as Google’s QUIC servers and some other projects.