Update enhanced prepared statements to use combined prepare & execute

Recent updates to Enhanced Prepared statements RFC to include a combined prepare and execute operation need to be added to the SDK.

Update from RFC owner (Michael N.):

Long promised, finally here – the (hopefully) final update to the enhanced prepared statements RFC.

The RFC has been updated, please re-read this chapter: https://docs.google.com/document/d/1JhprmvL2HwHzkg7GxouGJc67eAvKFJekgyOG23T8mVU/edit#heading=h.jyt1um891uu

It covers the new fast-prepare support, you can find more about it here too: https://docs.google.com/document/d/11w93jq_a6sAYqcJG5roIKAYm7WGTBD-obr9hqQTe9Ck/edit

TL;DR:

Prepare and execute are replaced with a single operation, which works as described in the document

This helps us to cut down to a single operation even in the case where the cache is not primed with the given statement

The java implementation for reference can be found in this gerrit change: http://review.couchbase.org/#/c/113494/