Summary:
Ref T9979. I picked this name long before the advent of modern "Engine" architecture and it ended up being pretty confusing.
Rename "SearchEngine" (currently: mysql or elasticsearch, used to store and query fulltext indexes) to "FulltextStorageEngine" to make it more clear what it does and disambituate it from ApplicationSearch, which also has a bunch of stuff called "SearchEngine", "SearchEngineExtension", etc.
Test Plan: Grepped for `phabricatorsearchengine`.
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T9979
Differential Revision: https://secure.phabricator.com/D14843
