msg: Add stdout/stderr filters

Add logging filters which can be used to split output between stdout and
stderr, ERROR messages and above as passed by the Err filter, anything
below ERROR is passed by the Out filter. This is useful when trying to make
stderr more useful.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
knotty: Ensure the progress bar shows on stdout

I can understand why some programs would want the progress on stderr so
that real output can be captured on stdout. This is confusing for bitbake
since we don't show a progress bar at all in non-interactive cases.

Therefore make sure the progress bar goes to stdout, not the stderr default.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
knotty: Split error output onto stderr

When using bitbake -e in scripts, it would be helpful if the error
output appeared on stderr, not stdout. This change enables that building
upon the new bb.msg filters.

[YOCTO #5274]

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>