Implement custom jet fume functionality

This adds the skin flag SF_JETFUME, which causes the follow item to act like Metal Sonic's jet fume.

What was changed:

• When dash mode is entered, the follow object switches to its melee state.
• If MF2_FRET is set, the custom jet fume flashes during dash mode.
• If MF2_AMBUSH, the custom jet fume turns during the player's skid animation.
  • This now checks if the player is in their skid animation, rather than when skidtime is set.
• If MF2_JUSTATTACKED is set, the custom jet fume will cycle through the usual dash mode colors.

Notes:

• colorized is not automatically set on the custom jet fume. This can be done through a Lua script, or using A_Dye in SOC.
  • Note that doing the latter will obligatorily set the object's color due to how it works.
• MF2_LINKDRAW is not automatically set. This is easy to enable through SOC or a Lua script.

This example WAD demonstrates how SOC can be used to create a follow item similar to Metal Sonic's jet fume.
jet-fume-example.wad

Resolves #1391 (closed).