Fix wrong coordinates for pixel-register and shape

[leouieda]

Fix a bug in grid_coordinates when passing pixel_register=True and
shape instead of spacing. The returned coordinates had 1 too few
elements in each dimension (and the wrong values). This is because we
generate grid-line registered points first and then shift them to the
center of the pixels and drop the last point. This only works when
specifying spacing because it will generate the right amount of
points. When shape is given, we need to first convert it to
"grid-line" shape (with 1 extra point per dimension) before generating
coordinates.

Reminders

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst and verde/__init__.py.
• Write detailed docstrings for all functions/classes/methods.
• If adding new functionality, add an example to the docstring, gallery, and/or tutorials.