Add new mushroom base terrain and make the overlay have mixed defense (#4299)

Thanks to @doofus-01 for the mycelium terrain graphics.

data/core/terrain-graphics.cfg

@@ -152,7 +152,7 @@ C*,K*,X*,Q*,W*,Ai,M*,*^V*,*^B*,_off^_usr#enddef
 {NEW:FOREST             H*^Fma,M*^Fma   {SMALL_FOREST_FILTER}  forest/mixed-winter-snow-sparse}
 {NEW:FOREST             *^Fma           {SMALL_FOREST_FILTER}  forest/mixed-winter-snow}
 
-{NEW:FOREST             *^Uf*           {SMALL_FOREST_FILTER}  forest/mushrooms}
+{NEW:FOREST             (*^Uf*,*^Tf*)   {SMALL_FOREST_FILTER}  forest/mushrooms}
 
 #undef SMALL_FOREST_FILTER
 
@@ -350,7 +350,7 @@ C*,K*,X*,Q*,W*,Ai,M*,*^V*,*^B*,_off^_usr#enddef
 {NEW:FENCE *^Eff embellishments/fence}
 
 # Illuminated caves
-{NEW:OVERLAY             (*^Ufi,*^Ii)                                              cave/beam FLAG=light LAYER=1}
+{NEW:OVERLAY             (*^Ufi,*^Ii,*^Tfi)                                              cave/beam FLAG=light LAYER=1}
 
 # Wall sconces or torches
 {NEW:WALL_FLAMES_OVERLAY (X*^Efs)							walls/stone/flames/sconce}
@@ -439,6 +439,7 @@ C*,K*,X*,Q*,W*,Ai,M*,*^V*,*^B*,_off^_usr#enddef
 #
 
 # Flat base terrains
+{NEW:BASE                Tb                                forest/mushroom-base LAYER=-319}
 
 # The first grass tile of each kind is the most standard and generic one, thus it appears more frequently to space out the rest
 {NEW:BASE_P              Gg                                     20                 grass/green}
@@ -841,6 +842,9 @@ C*,K*,X*,Q*,W*,Ai,M*,*^V*,*^B*,_off^_usr#enddef
 {NEW:TRANSITION            (Ms,Ha)          (W*,S*)                     -171               hills/snow-to-water}
 {NEW:TRANSITION            (Ms,Ha)          (!,Ha,Qx*,Mm,Ms,Md)         -172               hills/snow}
 
+{NEW:TRANSITION            (Tb)             (!,M*,Tb)                   -184               forest/mushroom-base}
+{NEW:DISABLE_TRANSITION    (R*,G*,H*,U*,A*) (*^Uf*,*^Tf*)}
+{NEW:DISABLE_TRANSITION    (R*,G*,H*,U*,A*) (*^Uf*,*^Tf*) FLAG=inside}
 {NEW:TRANSITION            (Mm,Hh)          (!,M*,Hh,Ai,W*,S*)          -180               hills/regular}
 {NEW:TRANSITION            (Md,Hhd)         (!,M*,Hhd,Ai,W*,S*)         -183               hills/dry}
 {NEW:TRANSITION            Hd               (!,Hd,Qx*,W*)               -184               hills/desert}

data/core/terrain.cfg

@@ -940,13 +940,39 @@ Most units receive 20 to 40% defense in sand."
 
 [terrain_type]
     symbol_image=forest/mushrooms-tile
-    id=fungus_grove
+    id=fungus_grove_old
     name= _ "Mushroom Grove"
     editor_name= _ "Mushroom Grove"
     string=^Uf
-    aliasof=Uft
+    aliasof=Tt
     default_base=Uu
     editor_group=cave, forest
+    hidden=yes # deprecated, only kept around so old maps still work
+[/terrain_type]
+
+[terrain_type]
+    symbol_image=forest/mushrooms-beam-tile
+    id=fungus_beam_old
+    name= _ "Mushroom Grove"
+    editor_name= _ "Lit Mushroom Grove"
+    string=^Ufi
+    default_base=Uu
+    aliasof=Tt
+    light=25
+    editor_group=cave
+    hidden=yes # deprecated, only kept around so old maps still work
+[/terrain_type]
+
+[terrain_type]
+    symbol_image=forest/mushrooms-tile
+    id=fungus_grove
+    name= _ "Mushroom Grove"
+    editor_name= _ "Mushroom Grove"
+    string=^Tf
+    aliasof=_bas,Tt
+    mvt_alias=-,_bas,Tt
+    default_base=Tb
+    editor_group=cave, forest
 [/terrain_type]
 
 [terrain_type]
@@ -954,13 +980,24 @@ Most units receive 20 to 40% defense in sand."
     id=fungus_beam
     name= _ "Mushroom Grove"
     editor_name= _ "Lit Mushroom Grove"
-    string=^Ufi
-    default_base=Uu
-    aliasof=Uft
+    string=^Tfi
+    default_base=Tb
+    aliasof=_bas,Tt
+    mvt_alias=-,_bas,Tt
     light=25
     editor_group=cave
 [/terrain_type]
 
+[terrain_type]
+    symbol_image=forest/mushroom-base
+    id=fungus_floor
+    name= _ "Mycelium"
+    editor_name= _ "Mycelium"
+    string=Tb
+    aliasof=Tt
+    editor_group=cave
+[/terrain_type]
+
 [terrain_type]
     symbol_image=cave/hills-variation
     id=rocky_cave
@@ -2721,7 +2758,7 @@ For those who go by land or sea, a bridge is the best of both worlds — for gam
     id=fungus
     name= _ "Fungus"
     editor_name= _ "Fungus"
-    string=Uft
+    string=Tt
     hidden=yes
     help_topic_text= _ "<italic>text='Mushroom groves'</italic> are vast underground forests of giant mushrooms, which thrive in the damp darkness. Most units have trouble negotiating the spongy floor of smaller fungi, but they have plenty of cover behind the larger stalks. Mounted units, however, become completely mired and lack proper freedom of movement in combat. Undead units have a natural affinity for decay and function quite well in mushroom forests.