parallel solver: various changes

- threading: adding btSequentialImpulseConstraintSolverMt
 - task scheduler: added parallelSum so that parallel solver can compute residuals
 - CommonRigidBodyMTBase: add slider for solver least squares residual and allow multithreading without needing OpenMP, TBB, or PPL
 - taskScheduler: don't wait for workers to sleep/signal at the end of each parallel block
 - parallel solver: convertContacts split into an allocContactConstraints and setupContactConstraints stage, the latter of which is done in parallel
 - parallel solver: rolling friction is now interleaved along with normal friction
 - parallel solver: batchified split impulse solving + some cleanup
 - parallel solver: sorting batches from largest to smallest
 - parallel solver: added parallel batch creation
 - parallel solver: added warmstartingWriteBackContacts func + other cleanup
 - task scheduler: truncate low bits to preserve determinism with parallelSum
 - parallel solver: reducing dynamic mem allocs and trying to parallelize more of the batch setup
 - parallel solver: parallelize updating constraint batch ids for merging
 - parallel solver: adding debug visualization
 - task scheduler: make TBB task scheduler parallelSum deterministic
 - parallel solver: split batch gen code into separate file; allow selection of batch gen method
 - task scheduler: add sleepWorkerThreadsHint() at end of simulation
 - parallel solver: added grain size per phase
 - task Scheduler: fix for strange threading issue; also no need for main thread to wait for workers to sleep
 - base constraint solver: break out joint setup into separate function for profiling/overriding
 - parallel solver: allow different batching method for contacts vs joints
 - base constraint solver: add convertJoint and convertBodies to make it possible to parallelize joint and body conversion
 - parallel solver: convert joints and bodies in parallel now
 - parallel solver: speed up batch creation with run-length encoding
 - parallel solver: batch gen: run-length expansion in parallel; collect constraint info in parallel
 - parallel solver: adding spatial grid batching method
 - parallel solver: enhancements to spatial grid batching
 - sequential solver: moving code for writing back into functions that derived classes can call
 - parallel solver: do write back of bodies and joints in parallel
 - parallel solver: removed all batching methods except for spatial grid (others were ineffective)
 - parallel solver: added 2D or 3D grid batching options; and a bit of cleanup
 - move btDefaultTaskScheduler into LinearMath project

examples/MultiThreadedDemo/CommonRigidBodyMTBase.h

@@ -14,6 +14,7 @@
 enum SolverType
 {
     SOLVER_TYPE_SEQUENTIAL_IMPULSE,
+    SOLVER_TYPE_SEQUENTIAL_IMPULSE_MT,
     SOLVER_TYPE_NNCG,
     SOLVER_TYPE_MLCP_PGS,
     SOLVER_TYPE_MLCP_DANTZIG,
@@ -27,6 +28,7 @@ inline const char* getSolverTypeName( SolverType t )
     switch (t)
     {
     case SOLVER_TYPE_SEQUENTIAL_IMPULSE: return "SequentialImpulse";
+    case SOLVER_TYPE_SEQUENTIAL_IMPULSE_MT: return "SequentialImpulseMt";
     case SOLVER_TYPE_NNCG: return "NNCG";
     case SOLVER_TYPE_MLCP_PGS: return "MLCP ProjectedGaussSeidel";
     case SOLVER_TYPE_MLCP_DANTZIG: return "MLCP Dantzig";