Make Array.ASSIGN-POS about 15% faster (#4170)
Make Array.ASSIGN-POS about 15% faster (#4170)

By reducing the actual fast path to a single nqp::assign, and reworking
the tests into ternaries.  Also returns the actual container now rather
than a deconted value (just like Hash::ASSIGN-KEY does).

Eliminates the FAST-PATH private method.  Removes the index < 0 check
from the SLOW-PATH as that is now being checked in the actual ASSIGN-POS
method (but not really acted upon, just used as a flag to take the slow
path).
MasterDuke17/rakudo,rakudo/rakudo,rakudo/rakudo,labster/rakudo,tony-o/rakudo,labster/rakudo,tony-o/rakudo,tony-o/rakudo,tony-o/rakudo,labster/rakudo,MasterDuke17/rakudo,MasterDuke17/rakudo,MasterDuke17/rakudo,salortiz/rakudo,salortiz/rakudo,labster/rakudo,rakudo/rakudo,salortiz/rakudo,MasterDuke17/rakudo,salortiz/rakudo,salortiz/rakudo,salortiz/rakudo,tbrowder/rakudo,rakudo/rakudo,tbrowder/rakudo,rakudo/rakudo,MasterDuke17/rakudo,labster/rakudo,labster/rakudo,tony-o/rakudo,tbrowder/rakudo,tony-o/rakudo,tbrowder/rakudo,tbrowder/rakudo,rakudo/rakudo,tbrowder/rakudo