MP: unique background graphics for Isar's Cross

Mainlined from the add-on "Visual Map Pack"

changelog.md

@@ -5,6 +5,7 @@
  ### Campaigns
  ### Multiplayer
    * Added `/roll N` command to multiplayer games and game lobbies which produces a publicly visible random integer number ranged from 1 to N inclusively (issue #5221, PR #5326).
+   * Isar’s Cross got map background graphics, mainlined from the Visual Map Pack on 1.14
  ### Packaging
   * SDL_Image 2.0.2 or later is now required (was 2.0.0).
  ### Terrain

data/core/about.cfg

@@ -693,7 +693,7 @@
     [/entry]
     [entry]
         name = "Lukasz Wawrowski (inferno8)"
-        comment = "Drake attack icons with fmunoz"
+        comment = "Drake attack icons with fmunoz and map backgrounds for Isar’s Cross"
     [/entry]
     [entry]
         name = "Lordlewis"

data/multiplayer/scenarios/4p_Isars_Cross.cfg

@@ -59,4 +59,116 @@
         gold=75
         fog=yes
     [/side]
+
+    [options]
+        [checkbox]
+            id=simple_background
+            default=no
+            name= _ "Disable Background Image"
+            # po: Tooltip for the Isar's Cross map, makes the map look as it did in Wesnoth 1.14 and earlier
+            description= _"Show a blank area outside the map, instead of the floating island with cliffs."
+        [/checkbox]
+    [/options]
+
+    [event]
+        name=prestart
+
+        [if]
+            [variable]
+                name=simple_background
+                boolean_equals=no
+            [/variable]
+            [then]
+                [terrain]
+                    x,y=1,1
+                    terrain=Xv^Xo
+                [/terrain]
+                [lift_fog]
+                    terrain=Xv^*,_off^_usr
+                    multiturn=yes
+                [/lift_fog]
+            [/then]
+        [/if]
+        # not clearing the variable (if set), leaving it for add-ons
+    [/event]
+
+    [terrain_graphics]
+        [image]
+            layer=0
+            name=map-specific/isar-background.png
+            center=792,1062
+            [variant]
+                tod=first_watch,second_watch
+                layer=0
+                name=map-specific/isar-background-night.png
+                center=792,1062
+            [/variant]
+            [variant]
+                tod=dawn,dusk
+                layer=0
+                name=map-specific/isar-background-dawndusk.png
+                center=792,1062
+            [/variant]
+        [/image]
+        [tile]
+            pos=1
+            type=*^Xo
+        [/tile]
+        map="
+,*,*,*,*,*,*,*,*,*,*,*,*,*,*
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+*,*,*,*,*,*,*,*,*,*,*,*,*,*,*
+,*,*,*,*,*,*,*,*,*,*,*,*,*,*"
+    [/terrain_graphics]
 [/multiplayer]