fix: Recalculate bounding boxes after fonts load

[camdecoster]

Description

Recalculate bounding boxes after fonts load to ensure they are sized properly.

Closes #8089.

Changes

• Track which fonts aren't loaded yet and redraw when they settle
• Clean up tracking token during purge
• Add tests
• Update internal type
• Add utility for parsing font families

Screenshots

Before	After

Testing

• Be on main
• Open plotly devtools and paste the following into the browser devtools console:

  // A new family and URL on every run, so the plot always draws before the font arrives
  const family = `JetBrainsMono${Date.now()}`;
  const face = new FontFace(
      family,
      `url(https://cdn.jsdelivr.net/npm/@fontsource/[email protected]/files/jetbrains-mono-latin-400-normal.woff2?v=${Math.random()})`
  );
  document.fonts.add(face);
  
  const gd = Tabs.fresh();
  Plotly.newPlot(
      gd,
      [
          { type: 'bar', x: ['NO', 'DE', 'CA'], y: [30, 12, 10], name: 'Gold: a test of sizes' },
          { type: 'bar', x: ['NO', 'DE', 'CA'], y: [8, 10, 5], name: 'Silver: a second test of sizes' }
      ],
      {
          font: { family, size: 13 },
          legend: { borderwidth: 1, x: 0.02, y: 0.98 },
          width: 500,
          height: 300,
          annotations: [
              {
                  x: 1.02, y: 0, xref: 'paper', yref: 'paper', xanchor: 'left', yanchor: 'bottom',
                  text: 'Source: official list', textangle: -90, showarrow: false,
                  bgcolor: 'rgba(0,0,0,0.15)', borderwidth: 1
              }
          ]
      }
  );

• Note that the text boxes have the incorrect sizes
• Switch to this branch
• Run the snippet again
• Note that the text boxes have the correct sizes

Notes

• The first draw is synchronous, so plots with no specified fonts shouldn't see any change with this update
• Plots with fonts specified that are drawn before the fonts load will be redrawn after those fonts load
  • The redraw costs about as much as the first draw
  • It happens once per font load
  • Here are some performance numbers from Chrome running locally:

    Plots	First draw	Redraws after the font loads
    1 small bar chart	18 ms	21 ms
    20 small bar charts (3 runs)	112-139 ms	94-185 ms
    1 plot with a 50,000-point SVG scatter	596 ms	593 ms
    20 plots with a 5,000-point SVG scatter each	1.6 s	1.3 s

  • The redraws run synchronously in one task.
• Plots with fonts specified that are drawn after the fonts load will be drawn once with the correct sizes
• Purged plots don't get redrawn
• The redraw fires plotly_beforeplot and plotly_afterplot again
• To skip the extra draw, wait for the font before the first draw:

  await document.fonts.load('12px "Open Sans"');
  await Plotly.newPlot(gd, data, layout);

• document.fonts.ready does not work for this, because ready does not start the load of a font that no text uses yet
• A WebKit bug prevents use of the loadingdone event on the document fonts
• This fix does not cover text drawn on a canvas, such as scattergl text and gl3d labels. A plot redraws only when an SVG element in the plot uses the loaded family.
• This fix is related to Axis labels and tick labels in 3D plots do not use fonts loaded from remote server #7413, but it doesn't actually fix that issue. gl-axes3d caches each label mesh by font family for the life of the page, so gl3d labels keep the fallback font after the redraw.