swift234

[stdlib] Improve efficiency of Array literals

Before this change, the dispatching hacks sent convertFromArrayLiteral
through the "Sequence" path, wherein we could not assume the ability to
non-destructively measure the length of the Sequence before beginning to
add the elements, which resulted in buffer reallocations as elements
were added.  Now we the sequence is measured and storage is
pre-allocated.

Swift SVN r18603