Add JNI StaticLayout.Builder

This patch adds a native C++ Builder object for StaticLayout to
complement the Java one introduced in a previous patch.

The Builder object contains state used in constructing a layout, as well
as temporary buffers, to avoid having to allocate such. In particular,
it holds a break iterator, so avoids the cost of constructing that in
the common case of a single locale.

Change-Id: I1125103b7ccf00b8674c1586c3ea8d5d915fdd5b