binderThroughputTest: add flag to dump raw data

When analyzing the output of `binderThroughputTest`, it can be useful to
export the raw data so that it can be manually analyzed later. It is
also useful for combining multiple runs of the benchmark into one.

Test: adb shell /data/local/tmp/binderThroughputTest -w 2 -s 0 -i 100000 -p -d /data/local/tmp/out
Change-Id: Id223f7f66d7d39f77ac5a12e82dfadd139d44c7f
Signed-off-by: Alice Ryhl <aliceryhl@google.com>