swift234

[SR-610][stdlib] Use _initialize_to in _copyCollectionToNativeArrayBuffer

The Generator interface is specialized for iteration and is often faster than indexing.

Using _initialize_to results in a ~10% speedup for Dictionary. For collections with more complex iteration state (such as search trees with O(log(n)) indexing), this leads to a complexity class improvement.

This requires a small change to the testsuite, because the generate() method of Defaulted*RangeReplaceableSlice called Array(self), which now leads to infinite recursion.

https://bugs.swift.org/browse/SR-610