This adds a small test case which maps a sub region of a small
attribute buffer and replaces the texture coordinates of one of the
vertices. The vertices are then drawn and the correct colours are
checked.
There is now a new test requirement for the
COGL_FEATURE_ID_MAP_BUFFER_FOR_WRITE feature which this test requires.
Reviewed-by: Robert Bragg <robert@linux.intel.com>
(cherry picked from commit 22183265b021dd038338b4398056c0a1eae77edb)
