Making x-grid great again

[dscso]

When updating from 1.2 to 2.0 x-grid doesn't work anymore. Here a practical example:

canvas({
    import draw: *

    plot.plot(
        size: (8,6),
        x-grid: true,
        y-grid: true,
        {
            plot.add(domain: (0, 2*calc.pi), calc.sin, label: $ sin x $)
            plot.add(domain: (0, 2*calc.pi), calc.cos, label: $ cos x $)
        }
    )
})

image

before

after this pull request

These are the tests that are different due to the change of this commit:
https://github.com/johannes-wolf/cetz/blob/master/tests/chart/ref.png
https://github.com/johannes-wolf/cetz/blob/0.2.0/tests/chart/ref.png
and
https://github.com/johannes-wolf/cetz/blob/master/tests/plot/ref.png
https://github.com/johannes-wolf/cetz/blob/0.2.0/tests/plot/ref.png
and
https://github.com/johannes-wolf/cetz/blob/master/tests/axes/ref.png
https://github.com/johannes-wolf/cetz/blob/0.2.0/tests/axes/ref.png

This pull request does fix this issue of the x-grid missing. All tests work except the three above mentioned.

[johannes-wolf]

Can you submit the updated test images by running just update-test?
If not, I'll do that in a later PR.

[johannes-wolf]

Thank you :)