Bug/pikul standoff position

[ayjayt]

https://github.com/plotly/plotly.js/issues/6890

Breakdown of the fix:

ax._depth is not calculated properly in the standoff conditional:

https://github.com/plotly/plotly.js/blob/5025fbc75b636a02d16320e7b4ff054f1fe6c301/src/plots/cartesian/axes.js#L2647-L2651

Lots of positioning calculations rely on that getLabelLevelBbox() which, bypassing the cache, is this:

function calcLabelLevelBbox(ax, cls) {
    var top, bottom;
    var left, right;

    if(ax._selections[cls].size()) {
        ... // iterate over ticklabels and get their DOM properties
    } else {
        top = bottom = left = right = 0;
    }

    return { top: top, bottom: bottom, left: left, right: right, height: bottom - top, width: right - left };
}

The issue being the else branch, where we have no ticklabels on which to loop. We shouldn't return 0 as null- 0 is a legitimate coordinate and will fool consumers. Instead, if we accept that an empty bounding box still has a position, but with a width and height of 0, we can calculate said position (where the ticklabel would be) and return a bounding box with no width or height. That's what I do in the fix using makeLabelFns(), and it seems to work well.

https://github.com/plotly/plotly.js/blob/236e9a37b792e507f96b4e7488927b4f25d9d7a0/src/plots/cartesian/axes.js#L2900-L2902

Let's see if these initial commits past the tests. Probably get rid of the mocks?