R1:add103810989

Don't summon the emoji autocompleter for ":3"

Summary:
Fixes T12460. Also ":)", ":(", ":/", and oldschool ":-)" variants.

Not included are variants with actual letters (`:D`, `:O`, `:P`) and obscure variants (`:^)`, `:*)`).

Test Plan: Typed `:3` (no emoji summoned). Typed `:dog3` (emoji summoned). Typed `@3` (user autocomplete summoned).

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12460

Differential Revision: https://secure.phabricator.com/D17577