tests/color-icc-output: add blending test

This is adding basically a copy of alpha-blending-test.c. The difference
is that here we use ICC files to set up the output color profile, and
then test light-linear blending only. BLOCK_WIDTH is set to 1 to fit
inside the output size used by the fixture setup, which is smaller than
in the original, but does not change the results.

The test is aimed at testing how color-lcms module succeeds in
linearizing the output of different ICC output profiles. Incorrect
linearization should cause changes in blending results.

The tolerance is taken from the currently achieved error statistics
(1.40908) and rounded up a little to achieve a suitable margin.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>