Improves:
* refactor: split CostAdjuster logic in multiple parts - prepare X, prepare cost, increase cost, reduce cost;
* refactor: improved VariableManaCost to support min/max values, playable and AI calculations, test framework;
* refactor: improved EarlyTargetCost to support mana costs too (related to #13023);
* refactor: migrated some cards with CostAdjuster and X to EarlyTargetCost (Knollspine Invocation, etc - related to #13023);
* refactor: added shared code for "As an additional cost to cast this spell, discard X creature cards";
* refactor: added shared code for "X is the converted mana cost of the exiled card";
* tests: added dozens tests with cost adjusters;
Bug fixes:
* game: fixed that some cards with CostAdjuster ignore min/max limits for X (allow to choose any X, example: Scorched Earth, Open The Way);
* game: fixed that some cards ask to announce already defined X values (example: Bargaining Table);
* game: fixed that some cards with CostAdjuster do not support combo with other cost modification effects;
* game, gui: fixed missing game logs about predefined X values;
* game, gui: fixed wrong X icon for predefined X values;
Test framework:
* test framework: added X min/max check for wrong values;
* test framework: added X min/max info in miss X value announce;
* test framework: added check to find duplicated effect bugs (see assertNoDuplicatedEffects);
Cards:
* Open The Way - fixed that it allow to choose any X without limits (close#12810);
* Unbound Flourishing - improved combo support for activated abilities with predefined X mana costs like Bargaining Table;
* [SLD] Implement Captain America, First Avenger
I made assumptions that WotC is going to fix the rules by adding "choose the equipment you're unattaching with Throw..." to rule 601.2b so that this card actually functions since you have to choose a TargetAnyTargetAmount in steps 601.2c/601.2d long before you actually pay the unattach cost in 601.2h.
* Remove Target workaround, add proper 601.2b handling for choosing cost targets early using inheritance to avoid having a horrific brittle list of 'these costs must be paid early'.
