Healer Support Micro AI: add optional SUF for healers

If set, only units passing this filter and having the healing ability
are used as healers.

data/ai/micro_ais/ais/mai_healer_support_engine.lua

@@ -93,12 +93,12 @@ return {
             cfg = cfg or {}
 
             local healers = wesnoth.get_units { side = wesnoth.current.side, ability = "healing",
-                formula = '$this_unit.moves > 0'
+                formula = '$this_unit.moves > 0', { "and", cfg.filter }
             }
             if (not healers[1]) then return 0 end
 
             local healers_noMP = wesnoth.get_units { side = wesnoth.current.side, ability = "healing",
-                formula = '$this_unit.moves = 0'
+                formula = '$this_unit.moves = 0', { "and", cfg.filter }
             }
 
             local all_units = wesnoth.get_units{ side = wesnoth.current.side }

data/ai/micro_ais/ais/micro_ais_wml_tags.lua

@@ -155,9 +155,12 @@ function wesnoth.wml_actions.micro_ai(cfg)
         local cfg_hs = {}
         if (cfg.action ~= 'delete') then
             -- Optional keys
+            cfg = cfg.__parsed
             cfg_hs.aggression = cfg.aggression or 1.0
             cfg_hs.injured_units_only = cfg.injured_units_only
             cfg_hs.max_threats = cfg.max_threats
+
+            cfg_hs.filter = H.get_child(cfg, "filter")
         end
 
         -- Set up the CA add/delete parameters