GuardsSelection Extend: Unit will guard ally when cannot attack target under cursor, without rushing to enemy's face

[dnqbob]

Life improvement
Image Update:

[dnqbob]

The second commit: allow closest ally to be guarded when ally closest to target is too far away

[darkademic]

Hmm does this do something similar to our KeepsDistance trait? That will basically make the unit stay away from units it can't attack, when an attack order is given to other units in the same selection.

[dnqbob]

I didn't notice KeepsDistance here, feels very useful and simple as well.

[dnqbob]

Maybe a small benefit can bring in this PR compared to KeepsDistance is, when ordered to attack unattackable, healer unit will not stop healing and try move within range.

[dnqbob]

Actually, I think we can merge the function of KeepsDistance into GuardsSelection here: when there is nothing can be guarded at AttackGuard order, actor will move within range instead of doing nothing.