Flowfield pathing

[heinezen]

Implements basic flow-field pathfinding in the engine.

• [x] Field types
  • [x] Cost field
  • [x] Integration field
  • [x] Flow field
• [x] Pathfinding
  • [x] Portal node graph search with A*
  • [x] Line Of Sight pass
  • [x] Cost Integration pass
  • [x] Flow Field Pass
• [x] Documentation
• [x] Demo 0: Flow field show case
• [x] Demo 1: Grid with portals/sector based search
  • [x] Interactive setting of path

What's missing:

• Cost stamps
• Caching flow field results
• Better heuristics cost for portal node graph search
• Pass LOS/wavefront flags through portal
• Integration into game simulation (next PR)

[heinezen]

The interactive demo is now finished!

[TheJJ]

rebase pls

[heinezen]

@TheJJ Done