split `cgs.media.floorFirePS` into `cgs.media.firebombGroundFirePS` and `cgs.media.flamerGroundFirePS`

[illwieckz]

Feature request: split cgs.media.floorFirePS into cgs.media.firebombGroundFirePS and cgs.media.flamerGroundFirePS.

This would allow us to set a different ground fire effect for fires produced by firebomb and flamer.

As described there, the original ground fire used by both the flamer and the firebomb was too heavy on performances, the proposed re-implementation uses a complete redesign that is also expected to be also more realistic for a firebomb that works by firing multiple submunitions.

On the other hand, I like the “carpet of fire” effect and this would fit the flamer's groundfire:

[slipher]

I think performance problems can be alleviated by making sure to use entityMergable on the flame shaders (see https://github.com/UnvanquishedAssets/res-weapons_src.dpkdir/pull/33).