Dont set Spell Cost, let it fall back to State ManaCost for Text Changes

In ApiFactory, the cost is defined there

https://github.com/Card-Forge/forge/blob/b74c0b178f85b33db58a0c520c50e314bbb65a8a/forge-game/src/main/java/forge/game/ability/AbilityFactory.java#L190-L193

Using the State ManaCost.

But what if we let it pass `null` and then, later in the Spell Class, have it fall back to the State ManaCost, affected by TextChanges?

For this to work as it should, additional costs need to be extracted as Static Abilities.
(and the AI needs to be updated for this)

might be needed for this: #9241