FormatterFunc no longer extends Function or BiFunction

[nedtwigg]

This is a breaking change in the hierarchy of one of Spotless' deepest abstractions, but we've had no problems with it at all. From that point of view, this is a very dumb change.

I was just curious "what would break if I delete the extends Function ... BiFunction thing?", and the answer was, nothing. Nothing broke at all, not a single other code change was needed.

I'm not quite sure what to make of that, except that Java's idea of "target typing" is extremely practical. When I realized that we could make this change, I wasn't sure if we should do it or not. Here's how I see it:

• Pros: FormatterFunc is simpler without out it (technically...)
• Cons: It's an unnecessary breaking change, just because we can squeeze it in with the rest of 2.0 doesn't mean we have to
• Trump card: We can add it back later, and it wouldn't be a breaking change

@jbduncan just FYI

[jbduncan]

@nedtwigg Thanks for warning me about this change!

Yep, this is fine with me, given that with hindsight it's easy to target different functional interfaces with method references.

So LGTM. 👍