Allow emoji suggestions based on a match anywhere in the emoji name, but improve sorting

This is a more nuanced approach to resolving #135 (closed) that I'm happier with. Emoji that match your input anywhere in their shortcodes get suggested, so typing :think will still suggest things like :blobthinking:, but shortcodes that match at the start and shorter shortcodes will be prioritized. I think this makes it a bit easier to discover emoji without remembering their exact names.