Fix the issue that AI do not act when and after frozen

Current AI do not handle frozen status very well, it won't try to break the ice and may permanently forget their target after the ice-block melts away if the player is not nearby, then AI will just stand still.

This commit try to fix this strange behavior:

1. When the ice-block melt, try to reset the AI's target to the applier
2. Let tactical AI hit the ice-block, leaving the numb AI for now (because they are numb)
3. Let your own projectile hit you if you are encased in ice, so you could break ice by projectile.

This commit only provides a possible solution for this issue, and its potential impact should be evaluated.

Status changed to merged

mentioned in commit a57f781a