Goto Micro AI: add remove_movement option

By default, the MAI removes movement points from units even when they cannot find a hex to move to.  When this option is set to 'no' (default is 'yes'), this step is skipped, so that other candidate actions can take over.

This implements feature request #5580

data/ai/micro_ais/cas/ca_goto.lua

@@ -227,9 +227,12 @@ function ca_goto:execution(cfg, data)
         end
     end
 
+    local remove_movement = cfg.remove_movement
+    if (remove_movement == nil) then remove_movement = true end
+
     if closest_hex then
         AH.checked_move_full(ai, best_unit, closest_hex[1], closest_hex[2])
-    else
+    elseif remove_movement then
         AH.checked_stopunit_moves(ai, best_unit)
     end
 

data/ai/micro_ais/mai-defs/misc.lua

@@ -24,7 +24,7 @@ wesnoth.micro_ais["goto"] = function(cfg)
 	local required_keys = { "[filter_location]" }
 	local optional_keys = {
 		"[avoid]", "avoid_enemies", "[filter]", "ignore_units", "ignore_enemy_at_goal",
-		"release_all_units_at_goal", "release_unit_at_goal", "unique_goals", "use_straight_line"
+		"release_all_units_at_goal", "release_unit_at_goal", "remove_movement", "unique_goals", "use_straight_line"
 	}
 	local CA_parms = {
 		ai_id = 'mai_goto',