Support snippets that fill hole with a target

[pokey]

• Can say eg "snip null check air" if you have a snippet called "null check" and it will insert snippet with particular snippet hole filled with "air"
• Also support "snip null check air after bat" to insert after something
• Apply wrapper scope type for given hole
• Support "move" version?
• Cool use case would be initialising variables in constructor, eg "snip init air after bat" would add eg self.apple = apple; after statement bat
• Would be cool if you could "snip init air and bat and cap" to insert three initialisations
• Alternately providing list target should maybe try to fill out multiple holes with the given items 🤔
• Worth thinking through relationship to Smarter snippet holes #445