Use ThreadWorkPool to process physics step tasks in multiple threads. Collisions are all processed in parallel and solving impulses is
processed in parallel for rigid body islands.
Additional changes:
- Proper islands for soft bodies linked to active bodies
- All moving areas are on separate islands (can be parallelized)
- Fix inconsistencies with body islands (Kinematic bodies could link
bodies together or not depending on the processing order)
- Completely prevent static bodies to be active (it could cause islands
to be wrongly created and cause dangerous multi-threading operations as
well as inconsistencies in created islands)
- Apply impulses only on dynamic bodies to avoid unsafe multi-threaded
operations (static bodies can be on multiple islands)
- Removed inverted iterations when populating body islands, it's now
faster in regular order (maybe after fixing inconsistencies)
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