feat: make gibs fly away from damage, CVAR

[WofWca]

gib-directional-3.mp4

TODO:

• Address the TODOs in the comments
• Clean up the code.
• Add an easy way to disable this.
• Consider disabling by default.
• Find a good default value. 5 might be too much sometimes, and 1 or 2 can be too weak.
• (optional) fiddle with the way it works. Make damage-dependent.
• This MR is only about the last commit. The first one ("feat: GibPlayer: spread gib start positions") can be removed, or merged separately.

[ec-]

Looks very cool, config cvar (for strength/direction) is necessary for that

[WofWca]

Closing in favor of #53