I would like to suggest a few new spawn reasons (in the CreatureSpawnEvent) that are heavily geared towards new mechanics in MC 1.14
PILLAGER_OUTPOST: probably needs a better name, but when pillagers spawn at a Pillager outpost. (as per McWiki - Pillagers naturally spawn within a 64×64 block area around pillager outposts.)
RAID: For when a raider spawns as part of a raid (as per McWiki - Pillagers are able to spawn as part of raids, as the most common mob in one. Raids start when a player enters a village with Bad Omen.)
ILLAGER_PATROL: For when an Illager spawns due to an Illager Patrol (as per McWiki - 5 pillagers spawn in patrols. Patrols spawn naturally throughout the night but after 5 in-game days. They spawn independently of structures, including villages and illager outposts (i.e. they will still spawn in a "no structures" world).)
Thank you for reading!