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;
