AttackConstraints: turn Magnet Keyword into Static Abilities

[Northmoc]

          for later MR, can we turn the following Keywords into Static Abilities?

Originally posted by @Hanmac in #3589 (comment)

[Northmoc]

@tool4ever I'd be down to give this a try

[Hanmac]

Magnet Keyword is just one of them, but we could do that in smaller steps

Also there is this thing: #1424

The AttackRestrictionType Enum with hard coded color words is a thorn in my eye

[github-actions]

This issue has not been updated in a while and has now been marked as stale. Stale messages will be auto closed.

[Hanmac]

forge/forge-game/src/main/java/forge/game/combat/AttackConstraints.java

Lines 51 to 57 in e996dad

	final CardCollectionView magnetAttackers = CardLists.filter(possibleAttackers, CardPredicates.hasCounter(CounterEnumType.MAGNET));
	// Only require if a creature with a magnet counter on it attacks.
	if (!magnetAttackers.isEmpty()) {
	nMagnetRequirements = CardLists.getAmountOfKeyword(
	game.getCardsIn(ZoneType.Battlefield),
	"If a creature with a magnet counter on it attacks, all creatures with magnet counters on them attack if able.");
	}

this probably should be able to be put into a Static AttackRequirement mode,
with ValidCard (Card) + ValidAttacker (list - ValidCard)

then Magnet for example can do:
S:Mode$ AttackRequirement | ValidCard$ Card.counters_GE1_MAGNET | ValidAttacker$ Card.counters_GE1_MAGNET

I think the result should be something like causesToAttack = Multimap<Card, StaticAbility>

So that ValidAttacker should not be validated as list, more like a Filter.

Example: A, B and C have Magnet counters.
So their Multimap should look like A => [B => StAb, C => StAb], B => [A => StAb, C => StAb], C => [A => StAb, B => StAb]