simd4x4f: Fix look_at() implementation

There is no need to transpose the matrix before translating it to the
eye coordinates.

This breaks the matrix look_at() unit tests but I'm pretty confident
that it is correct because:

  • the same approach is used by various look_at() implementations,
    like the one in Cogl and Mesa

  • the change fixes users of graphene_matrix_look_at(), like Gthree

This seems to imply that the tests are incorrect, and they were testing
the wrong implementation.
tests/matrix: Rework the failing look_at() tests

The tests are checking the old, buggy implementation.

The rotation tests have the wrong sign for the angles, so they are
easily fixed.

The random eye, center, up test requires some more thought, so it's
currently disabled.