When we build up a matrix from a series of operations, it's very useful
to know if the combined operations still result in something that matches
a wl_output_transform.
This adds a function to test if a matrix leads to a standard output
transform, and returns the transform if it does.
Tests are provided that check if complex series of operations return
expected results - the weston_matrix_needs_filtering function is tested
at the same time.
Signed-off-by: Derek Foreman <derek.foreman@collabora.com>
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