Limit AI to cast Green Sun's Zenith for all its mana

[kojotak]

Second attempt to fix issue #6720, following the previous closed PR #9962. FYI @tool4ever

tl;tr: it's almost the same

• AI can be limited with new param AIMaxTgtCost to not over spent all X mana
• AI can be instructed to consider LeftoverMana in order filter payable creatures only

Seems OK for Green Sun's Zenith and similar Nature's Rhythm and Chord of Calling

It's still sub optimal for Finale of Devastation:

• limiting X for ChangeZone prevents spending 10+ mana for pump effect
• I tried to add AILogic$ PlayForSub, but this is either-or situation (not finding suitable creature will check PumpAllAi#chkDrawback, but this will leave X set to 0)
• I tried to add SVar:Z:Count$ValidBattlefield Creature.YouCtrl but I don't know how to combine it with X