Implement Gen 6 Symbiosis Eject Button glitch

[atauber27]

(https://github.com/smogon/pokemon-showdown/projects/3#card-61614976)
Implemented functionality for a specific interaction between an Eject Button holder and a Symbiosis user in Gen 6 doubles. If the Eject Button activates, the lastTurnEjected variable is updated to the turn on which the ejection occurred. Whenever this Pokemon switches out, if the current turn does not match the turn on which it was ejected (i.e. it switched back in, then out again) or if it is not holding an item (i.e. an item was not passed onto it via Symbiosis), lastTurnEjected is set to null. When lastTurnEjected is not null, a variety of effects occur:

• Choice items, Assault Vest, Eviolite, type-enhancing effects, etc. have their buffs applied twice, handled in battle.chainModify
• Black Sludge and Sticky Barb both affect the user twice, while Leftovers heals the user four times, implemented in batle.residualEvent
• Restorative berries and the Berry Juice heal the holder twice if they are not eaten upon switching in, implemented in pokemon.eatItem
• Stat stage boosting items, such as the Weakness Policy and Starf Berry, activate twice, implemented in pokemon.useItem
• Scope Lens and Razor Claw boost the holder's critical hit stage by 2, hard coded in data/mods/gen6/items
• Rocky Helmet damages the attacker twice on contact, hard coded in data/mods/gen6/items
• Destiny Knot activates twice to bypass the effects of Mental Herb, hard coded in data/mods/gen6/items (Mental Herb)
• Life Orb damages the user twice, but also applies the damage buff twice, handled in chainModify and data/mods/gen6/items
• Metronome applies each incremental damage modifier twice, handled in chainModify
• Shell Bell heals the user twice, hard coded in data/mods/gen6/items
• Damage-reducing berries cause the user to only take 1/4 of the original damage, handled in pokemon.eatItem and chainModify
• Quick Claw has its activation message display twice, hard coded in data/mods/gen6/items
• Air Balloon displays its floating message twice, hard coded in data/mods/gen6/items