Javadoc
In case the choice of mana to be produced is obvious, let's discard all
other abilities.
Example: Pay {W}{R}
Land produces {W} or {G}.
No need to ask what player wants to choose. {W} mana ability should be
left only.
But we CAN do auto choice only in case we have basic mana abilities.
Example: we should pay {1} and we have Cavern of Souls that can produce
{1} or any mana of creature type choice. We can't simply auto choose {1}
as the second mana ability also makes spell uncounterable.
In case we can't auto choose we'll simply return the useableAbilities map
back to caller without any modification.