[vector-api] Fix ol.geom.flat.linearRingContainsXY

This PR fixes a bug in for point-in-linear ring tests. The point-in-linear ring test was not taking into account the closing edge of the linear ring (i.e. from the last coordinate to the first).

Note: `master` may or may not contain the same bug. If `master` ensures that all linear rings are closed (i.e. that for every linear ring, the last vertex is equal to the first) then `master` does not have this bug. If `master` does not ensure this, then `master` has this bug.