Only convert the raw output later in a stdOut() and stdErr() method of
the SynchronousProcessResponse.

This is necessary since we have processes that use different encodings
for different sections of the file (I am looking at you, git).

Also remove the signals for raw data on stdout/stderr, leaving only the
signals returning buffered QString lines. This should be safe, even
with UTF-16 output.

Change-Id: Ida613fa86d1468cbd33bc6b3a1506a849c2d1c0a
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>