[lua] Refactor Reactive Shield

[Skold177]

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• I understand that if I do not agree to the following points by completing the checkboxes my PR will be ignored.
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• I have read and understood the Contributing Guide and the Code of Conduct.
• I have tested my code and the things my code has changed since the last commit in the PR and will test after any later commits.

What does this pull request do?

Refactors code in Reactive Shield with a more accurate power formula. Did some brief testing at Lv. 50, 60, 70 & 99 and came up with...

damage = math.floor((skill / 16( + (INT / 6))

It's not perfect, and will sometimes deliver damage 1-2 damage too low, but it's a massive improvement over what was there before. There may be a dINT component as well, but I left a TODO to verify it further.

ReactiveShield.zip

Lv.70
INT 54
251 Skill
22-24 Damage

Lv.60
INT 45
203 Skill
17-19 Damage

Lv.50
INT 38
153 Skill
14-15 Damage

Lv.99
INT 81
Skill 424
42-45 Damage

Lv.99
INT 81+77
Skill 424
53-56 Damage

Steps to test these changes

Equip Reactive Shield, use Fire Maneuvers, get Blaze Spikes.