support CSS line-height for Label font

[nmschulte]

• adds support for controlling line-spacing in multi-line Labels -- avoids needing separate labels and new-line/transparent-background/fill hacks for certain multi-line labeling visualizations
• changes multi-line Label line-spacing basis from per-label max-glyph-height to font-size -- e.g. when rendering a label with text "^1" at the same location as one with text "^", the carets will render at the same height (with certain alignments... i.e. left-bottom)
• tested to support "0" line-spacing, though I think the line-spacing codes can still be improved to be consistent with CSS behaviors/expectations -- see maxLineHeight (understood as "line's max glyph height", excl.s spacing) and how it interacts with otherLinesHeight ("height of other lines", incl.s spacing) and totalLineHeight ("height of all lines", incl.s spacing); I think some of this codes should simply always use the specified font-size -- this implicates how the background is drawn, and the present logic specializes on the first or last line to avoid an "extra" line-spacing

[cesium-concierge]

Thanks for the pull request @nmschulte!

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[nmschulte]

I question why line-spacing is based upon the maximum glyph height instead of the font-size.

[hpinkos]

Not quite sure either. Your calculation looks fine, but we just need to make sure letters than go below the base like like 'y' and 'g' don't overrun tall letters like 'T' on the line below it

[nmschulte]

The existing logic causes multi-line label "heights" to only be as tall as the tallest character in the string, instead of a fixed height based upon the font-size (which is how I understand CSS font-size to work).

So label with text _\n_\n_\n_ renders with effectively small "line-heights" compared to one with text M\nM\nM\nM.

[cesium-concierge]

Thanks again for your contribution @nmschulte!

No one has commented on this pull request in 30 days. Maintainers, can you review, merge or close to keep things tidy?

I'm going to re-bump this in 30 days. If you'd like me to stop, just comment with @cesium-concierge stop. If you want me to start again, just delete the comment.

[cesium-concierge]

Thanks again for your contribution @nmschulte!

No one has commented on this pull request in 30 days. Maintainers, can you review, merge or close to keep things tidy?

I'm going to re-bump this in 30 days. If you'd like me to stop, just comment with @cesium-concierge stop. If you want me to start again, just delete the comment.

[nmschulte]

@hpinkos is there anything I can do to get this included? Does the breaking/behavior change need more clarification, or just some close attention for consideration?

[hpinkos]

@nmschulte sorry, I just haven't had the bandwidth to get back to this. @kring or @lilleyse would you have time to review?

[kring]

This seems like a good change to me. I tried a bunch of things and didn't run into any problems. Thanks @nmschulte!