Blank lines around var/let

[Uncommon]

I like to have blank lines separating groups of var/let statements from other kinds of statements.

I'm taking a stab at implementing this myself, so I'm looking for some feedback on whether I'm on the right track. The angle I'm looking at right now is looping through file.structure.dictionary.substructure to collect a list of lines that have var/let statements (SwiftDeclarationKind.var***), and then making sure they're all surrounded by blank lines appropriately. Does that sound like a good approach?

[marcelofabri]

Implemented in #1471.