In copy-prop-arrays, indentify copies via OpCompositeInsert

When the original code copies an entire array or struct one element at a
time, this turns into a series of OpCompositeInsert instruction followed
by a store of the whole array.  We currently miss opportunities in copy
propagate arrays because we do not recognize this as a copy.

This commit adds code to copy propagate arrays to identify this code
pattern.

Also updates the performance passed to run array copy propagation.