Fix `/kill` behaving differently to `/minecraft:kill`

[zp4rker]

Information

This PR fixes #5842.

Details

Proposed fix:

• Use Damageable#damage(double) instead of Damageable#setHealth(double)
• Use Float.MAX_VALUE as that is what /minecraft:kill uses

Environments tested:

OS: Windows 11

Java version: Corretto-21.0.3.9.1

• [x] Most recent Paper version (1.20.6-147-ver/1.20.6@e41d44f)
• [x] CraftBukkit/Spigot/Paper 1.12.2 (Just tested successful killing, not trigger of advancement)
• [x] CraftBukkit 1.8.8 (Just tested successful killing, not trigger of advancement)

Demonstration:
Triggers minecraft:entity_hurt_player which was previously not being triggered as mentioned in #5842

[CyberFlameGO]

I thought it intentionally was different to vanilla behavior - this change would also break /kill bypassing god mode iirc

[zp4rker]

Thanks for pointing that out, it does indeed break when in god mode. If older versions had a damage cause, could just use that but doesn't seem they do. Other solution I can think of is to check for Float.MAX_VALUE since I can't think of any example of something other than /kill using that value.