Mass rename of .consume{,_iter}() to .move_iter()

cc #7887
Clean up some unused imports in tests
std: merge iterator::DoubleEndedIterator and DoubleEndedIteratorUtil
std: merge Iterator and IteratorUtil
std: Rename Iterator.transform -> .map

cc #5898
std: Iterator.take_ -> .take
std: Iterator.flat_map_ -> .flat_map
std: Iterator.chain_ -> .chain
std: Iterator.last_ -> .last
std: Iterator.len_ -> .len
std: Transform.find_ -> .find