[codecs] CodecFactory is open

CodecFactory was migrated from unspecified to "closed", but wasn't
intended to be "closed". This edits sdk history to "open", and adds
handle_unknown_method where needed.

Bug: 478359574
Change-Id: I71fe9fcef757c6562cb719887743f2c601b57acd
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1497179
API-Review: Adam Barth <abarth@google.com>
Commit-Queue: Dustin Green <dustingreen@google.com>
Reviewed-by: Adam Barth <abarth@google.com>
15 files changed