[3.13] Make Android streams respect the unbuffered (`-u`) option (GH-138806) (#139110)

Android pipes stdout/stderr to the log, which means every write to the log
becomes a separate log line. As a result, most practical uses of stdout/stderr
should be buffered; but it doesn't hurt to preserve unbuffered handling in case
it's useful.
(cherry picked from commit 0ac377ff23672ae7e2451f4cdfbe37c4efd464e7)

Co-authored-by: Malcolm Smith <smith@chaquo.com>