dragIn and switchIn being two separate functions is a weird historical
quirk that leads to inconsistencies in implementation.
The only reason they need to be separated is a Mold Breaker quirk:
1da65efb12
(This is now done with an `if` statement.)
This should fix a lot of Roar/Whirlwind mechanics issues from `dragIn`
being on outdated mechanics compared to `switchIn`.
Previously, battle queue stuff was just strewn around `battle.ts`.
This gives it a new home: `battle-queue.ts`.
This was intended to make `battle.ts` slightly more tractable, although
the difference is so small that maybe I shouldn't bother. Oh, well,
every little bit helps.
