Update arrowhead label positioning and use label dimensions

[gavin-ts]

Summary

Improves arrowhead positioning and handling of large arrowhead labels.

Details

• fixes render: measure arrowhead label text #183
• usually arrowhead labels are 1 or *, but the scenario of having longer arrowhead labels wasn't accounted for
• instead of assuming a 1 character size for arrowhead labels, measure the text and use that for placement
• update renderer's bounding box for arrowhead labels
• updates arrowhead positioning according to arrowhead size
• adds long_arrowhead_label test
• adds arrowhead_sizes_with_labels test
• Note: this is different than wip: Consider arrowhead for label position #1192 which is adjusting edge label position around arrowheads, but this is for arrowhead labels
• TODO use edge label dimensions to adjust dagre/elk spacing adjust edge spacing/minimum length #1214

before

after

long arrowhead before/after

new test before

new test after

[alixander]

very nice. just some nits. can you include a sketch test as well to make sure it works in sketch mode?

[ejulio-ts]

why are there so many cases updated? Specially, cases without arrowhead labels

[gavin-ts]

very nice. just some nits. can you include a sketch test as well to make sure it works in sketch mode?

added as a sketch test

[gavin-ts]

why are there so many cases updated? Specially, cases without arrowhead labels

updated d2target srcLabel and dstLabel to Text type

@@ -1227,10 +1221,8 @@
       "id": "(h.m.s -> a.f.g)[0]",
       "src": "h.m.s",
       "srcArrow": "none",
-      "srcLabel": "",
       "dst": "a.f.g",
       "dstArrow": "triangle",
-      "dstLabel": "",
       "opacity": 1,
       "strokeDash": 0,
       "strokeWidth": 2,

https://github.com/terrastruct/d2/pull/1207/files?file-filters%5B%5D=.go&file-filters%5B%5D=.pdf&show-viewed-files=true#diff-b014022cd772b25135d09ba644217b8da2b537c7b7a5d670a893d173a289d18cR455