AI prefers to attack with Stoneforge Mystic/Elvish Piper rather than activating their ability

**Describe the bug**
AI prefers to attack with creatures with activated ability "tap: put card on the battlefield" rather than activating its ability if doesn't have any big creatures on the battlefield:

- [ ] Stoneforge Mystic (even if it has Kaldra Compleat in its hand and activating the ability would deal more damage);
- [ ] Elvish Piper (even if it has big creatures in hands).

**To Reproduce**
Steps to reproduce the behavior:
1. AI casts Stoneforge Mystic and finds Kaldra Compleat
2. Player doesn't have any big creatures on the battlefield, he passes the turn
3. AI attacks with its Stoneforge Mystic

and

1. AI has Elvish Piper without summoning sickness and untapped Forest on the battlefield and Iona, Shield of Emeria in hands
2. Player doesn't have any big creatures on the battlefield
3. AI attacks with its Elvish Piper

**Expected behavior**
AI should activate Stoneforge Mystic's/Elvish Piper's ability as often as possible, priority should be higher

**Desktop**
OS: Windows 10
Java Version: 1.8.0_202-b08
Forge Version: 1.6.59-SNAPSHOT-10.28 - 1.6.64-SNAPSHOT-08.02

**Screenshots**