Send 'trapped' flag in requests for pokémon that are known trapped

- BattlePokemon#isLastChoice now checks whether this is the last non-fainted active pokémon in a team.
- BattlePokemon#tryTrap now accepts an argument that, if true, will hide the fact that a pokémon is trapped.
This should revert an small (annoying) change in the UI for locked moves introduced as a secondary effect in 8afc588e4.
- NEXT: Shadow Tag shouldn't activate the 'maybeTrapped' flag after the suspected Shadow Tagger has made a move.
Oh, nvm, I see what this is doing. `isLastActive` might be a better name.