Dragonfire shield charging, discharge and creation

[HarleyGilpin]

Implements the dragonfire shield, which had item definitions but no behaviour.

Referenced against the 2011 wiki revision

Shield

• Charging - every dragonfire and skeletal wyvern icy breath the shield absorbs adds a charge, up to 50. An uncharged shield becomes charged on the first one. Each charge adds one to its melee, ranged and summoning defences.
• Activate - the worn option spends a charge to breathe dragonfire back at the current target for up to 290, on a two minute cooldown, at up to twelve squares and over obstacles, granting Magic, Defence and Constitution experience. Dragons are immune.
• Inspect reports the charge count, Empty releases the lot and reverts to the tradeable uncharged shield.
• Charges are lost with the shield on death, worked out after items kept on death so a protected shield stays charged.

Creation

• Smith a draconic visage onto an anti-dragon shield at an anvil, needing 90 Smithing and a hammer, for 2000 Smithing experience.
• Or pay Oziach 1,250,000 coins to forge it. He had no dialogue at all before this, only the shop his definition points at.

Both produce the uncharged shield.

Supporting fixes

Each of these was reached, or made reachable, by the shield.

• Item.amount counted charges as a quantity. The guard only recognised item-value charges when the definition's starting charge count was above one, which it never is for something that starts empty. A twenty charge shield therefore looked like twenty items: items kept on death protected three of them and the rest dropped as a stack. Capacity now decides, which also covers satchels, tea flasks and enchanted headgear.
• Dragonfire reduction in Equipment read the wrong entity. It sat in a when (source) and used the attacker's shield and antifire, messaging the attacker. Unreachable while only npcs breathed dragonfire, but firing the shield woke it up and cut the wielder's own damage by 80% while telling them their shield had absorbed it. Dragonfire.maxHit already applies the victim's shield, potion and prayer, so the duplicate is gone and its shield message moved there, where it reaches the victim.
• Fire resistant shields did nothing against icy breath, from the same wrong-entity bug, and fireResistantShield compared against dragonfire_shield, an alias rather than an equipped id. The cap also replaced the damage rather than limiting it, so a small hit was raised to it. SkeletalWyvern now shares the one shield check instead of keeping its own copy.
• Player dragonfire granted Constitution experience alone, now Magic and Defence too.
• Dragonfire.maxHit returned -1 for an immune dragon, which would have thrown out of random.nextInt(0, 0) in Damage.roll as soon as a player could deal dragonfire.

Data

Shield definitions moved out of ancient_cavern.* into data/entity/player/equipment/dragonfire_shield.*, since it is not ancient cavern content.

Testing

20 tests across DragonfireShieldTest, OziachTest and IcyBreathTest covering charging and the cap, the defence bonus, activate with its cooldown, range and dragon immunity, inspect and empty, death conversion, both creation routes and their requirements, and the icy breath cap. Full suite green.

One test changed: EnchantedHeadgearTest asserted a helm's stored scroll count through Item.amount, now read through charges().