Propagate "create if missing"-flag outside binary Update payload in protocols

Avoids potentially having to deserialize the entire update just
to get to a single bit of information that is technically
metadata existing orthogonally to the document update itself.

To ensure backwards/forwards compatibility, the flag is
propagated as a Protobuf `enum` where the default value is
a special "unspecified" sentinel, implying an old sender.

Since the Java protocol implementation always eagerly
deserializes messages, it unconditionally assigns the
`create_if_missing` field when sending and completely ignores
it when receiving.

The C++ protocol implementation observes and propagates the
field iff set. Otherwise the flag is deferred to the update
object as before. This applies to both the DocumentAPI and
StorageAPI protocols.

1 files changed, 0 insertions, 0 deletions

diff --git a/documentapi/test/crosslanguagefiles/8.310-java-UpdateDocumentMessage.dat b/documentapi/test/crosslanguagefiles/8.310-java-UpdateDocumentMessage.dat
index f1ceef0e51a..fc42a504f8b 100644
--- a/documentapi/test/crosslanguagefiles/8.310-java-UpdateDocumentMessage.dat
+++ b/documentapi/test/crosslanguagefiles/8.310-java-UpdateDocumentMessage.dat