binder: add read/writeUint64Vector functions

Intended to help clean up a shoehorning of an vector<uint64_t>
into a Int64Vector in libgui/surfaceflinger.

Bug: 120504999
Test: boot
Test: 1 new libbinder_test, BinderLibTest.VectorSent
Change-Id: Ifd42f31d75565165dd652084298f16440e69ee74