[lua] Implement ENHANCES_ELEMENTAL_SEAL

[wccbuck]

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What does this pull request do?

Implements the item mod ENHANCES_ELEMENTAL_SEAL, seen on the mythic weapon Laevateinn, which adds bonus damage to elemental spells cast under the effect of Elemental Seal.

Steps to test these changes

!changejob BLM 99
!additem 18994 (laevateinn lv75, ele seal +10)

Put a print statement in xi.spells.damage.calculateEleSealMultiplier for eleSealMultiplier. When casting a nuke without Laevateinn equipped, with or without Elemental Seal active, the multiplier should be 1. With Laevateinn equipped and Elemental Seal active, the multiplier should be 1.1.