Enhance limb healing functionality (#55069)

Author: Venera3

doc/JSON_FLAGS.md

@@ -340,6 +340,8 @@ Some armor flags, such as `WATCH` and `ALARMCLOCK` are compatible with other ite
 ## Bodyparts
 
 - ```ALWAYS_BLOCK``` This nonstandard bodypart is always eligible to block in unarmed combat even if your martial arts don't allow such blocks.
+- ```ALWAYS_HEAL``` This bodypart regenerates every regen tick (5 minutes, currently) regardless if the part would have healed normally.
+- ```HEAL_OVERRIDE``` This bodypart will always regenerate its `heal_bonus` HP instead of it modifying the base healing step. Without `ALWAYS_HEAL` this still only happens when the part would have healed non-zero amount of damage.
 - ```IGNORE_TEMP``` This bodypart is ignored for temperature calculations
 - ```LIMB_LOWER``` This bodypart is close to the ground, and as such has a higher chance to be attacked by small monsters - hitsize is tripled for creatures that can't attack upper limbs.
 - ```LIMB_UPPER``` This bodypart is high off the ground, and as such can't be attacked by small monsters - unless they have the `FLIES` or have `ATTACK_UPPER` flags`

doc/JSON_INFO.md

@@ -649,7 +649,7 @@ For information about tools with option to export ASCII art in format ready to b
 | `temp_mod`             | (_optional array_) Intrinsic temperature modifier of the bodypart.  The first value (in the same "temperature unit" as mutations' `bodytemp_modifier`) is always applied, the second value is apllied on top when the bodypart isn't overheated.
 | `env_protection`       | (_optional_) Innate environmental protection of this part. (default: `0`)
 | `stat_hp_mods`         | (_optional_) Values modifying hp_max of this part following this formula: `hp_max += int_mod*int_max + dex_mod*dex_max + str_mod*str_max + per_mod*per_max + health_mod*get_healthy()` with X_max being the unmodified value of the X stat and get_healthy() being the hidden health stat of the character.
-| `heal_bonus`           | (_optional_) Innate amount of HP the bodypart heals every healing roll ( 5 minutes, currently ).
+| `heal_bonus`           | (_optional_) Innate amount of HP the bodypart heals every successful healing roll. See the `ALWAYS_HEAL` and `HEAL_OVERRIDE` flags.
 | `mend_rate`            | (_optional_) Innate mending rate of the limb, should it get broken. Default `1.0`, used as a multiplier on the healing factor after other factors are calculated. 
 | `health_limit`         | (_optional_) Amount of limb HP necessary for the limb to provide its melee `techniques` and `conditional_flags`.  Defaults to 1, meaning broken limbs don't contribute.
 | `bionic_slots`         | (_optional_) How many bionic slots does this part have.

src/character.cpp

@@ -277,6 +277,7 @@ static const itype_id itype_rm13_armor_on( "rm13_armor_on" );
 
 static const json_character_flag json_flag_ACID_IMMUNE( "ACID_IMMUNE" );
 static const json_character_flag json_flag_ALARMCLOCK( "ALARMCLOCK" );
+static const json_character_flag json_flag_ALWAYS_HEAL( "ALWAYS_HEAL" );
 static const json_character_flag json_flag_BASH_IMMUNE( "BASH_IMMUNE" );
 static const json_character_flag json_flag_BIO_IMMUNE( "BIO_IMMUNE" );
 static const json_character_flag json_flag_BLIND( "BLIND" );
@@ -291,6 +292,7 @@ static const json_character_flag json_flag_ELECTRIC_IMMUNE( "ELECTRIC_IMMUNE" );
 static const json_character_flag json_flag_ENHANCED_VISION( "ENHANCED_VISION" );
 static const json_character_flag json_flag_EYE_MEMBRANE( "EYE_MEMBRANE" );
 static const json_character_flag json_flag_FEATHER_FALL( "FEATHER_FALL" );
+static const json_character_flag json_flag_HEAL_OVERRIDE( "HEAL_OVERRIDE" );
 static const json_character_flag json_flag_HEATPROOF( "HEATPROOF" );
 static const json_character_flag json_flag_HEATSINK( "HEATSINK" );
 static const json_character_flag json_flag_HYPEROPIC( "HYPEROPIC" );
@@ -7526,10 +7528,21 @@ void Character::heal_bp( bodypart_id bp, int dam )
 
 void Character::heal( const bodypart_id &healed, int dam )
 {
-    if( !is_limb_broken( healed ) ) {
-        int effective_heal = std::min( dam + healed->heal_bonus,
+    if( !is_limb_broken( healed ) && ( dam != 0 || healed->has_flag( json_flag_ALWAYS_HEAL ) ) ) {
+        add_msg_debug( debugmode::DF_CHAR_HEALTH, "Base healing of %s = %d", body_part_name( healed ),
+                       dam );
+        if( healed->has_flag( json_flag_HEAL_OVERRIDE ) ) {
+            dam = healed->heal_bonus;
+            add_msg_debug( debugmode::DF_CHAR_HEALTH, "Heal override, new healing %d", dam );
+        } else {
+            dam += healed->heal_bonus;
+            add_msg_debug( debugmode::DF_CHAR_HEALTH, "Healing after bodypart heal bonus %d", dam );
+        }
+        int effective_heal = std::min( dam,
                                        get_part_hp_max( healed ) - get_part_hp_cur( healed ) ) ;
         mod_part_hp_cur( healed, effective_heal );
+        add_msg_debug( debugmode::DF_CHAR_HEALTH, "Final healing of %s = %d", body_part_name( healed ),
+                       dam );
         get_event_bus().send<event_type::character_heals_damage>( getID(), effective_heal );
     }
 }