Keep descenders of a text whole and frame it at its drawn size

A text was drawn into a texture as tall as Pixi measures the string
"|ÉqÅM". Whatever reached further, like the "g" of Manrope (0.015 em
below the "q"), was cut off at the bottom. The blue frame around a
text was only estimated from the font size and the number of letters,
so it was far too wide for most texts.

- textPicture.ts takes the height of a line from the font itself
  (fontBoundingBoxAscent and fontBoundingBoxDescent, as a browser
  does). Pixi draws with a margin, and the picture is cut to that box
  afterwards. Where Pixi's own box is larger, Pixi's box wins.
- Both raster paths (linear and nearest) use the cut.
- The height no longer depends on the letters typed, so a text does
  not jump while it is edited.
- bounds.ts asks a measurer that textPicture.ts registers
  (setTextMeasure). Selection, picking in a running game, framing the
  camera, the drop preview and culling all get the measured size.
  The footprint functions take the font file for this.
- Unit tests in node have no canvas and keep the estimate
  (estimatedTextSize).
- Texts get taller: Source Sans 3 at 48 px is 68 instead of 55 px,
  Manrope is 1.366 em instead of 1.25 em. The glyphs stay in place,
  the centre moves by less than half a pixel. A shader on a text
  gets a taller UV rectangle.

Tests:
- Gate on melektaus-atx green: 307 files, 4762 tests.
- 5 new unit tests for textBox, textCut and the measurer hook.
- e2e 30: 26 checks, 30f-iii new. The texture is 68 high, the font
  box is 68, the frame equals the drawn picture (237x68).
- Counter test: with Pixi's old box the texture is 55 high and
  30f-iii is red.
- Not checked in the browser: the Manrope caption of the user and
  texts with several lines.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/e2e/30-font.mjs

@@ -218,6 +218,26 @@ export async function font(t) {
     JSON.stringify({ plain: plain.width, wide: wide?.width, tight: tight?.width }),
   );
 
+  // 30f-iii. A text is as tall as its face's own line box, not as Pixi's "|ÉqÅM" reaches, so a
+  //          tail like Manrope's "g" stays whole – and the frame around it is the drawn picture.
+  const upright = await waitFor(info, (value) => value?.width === plain.width);
+  const lineBox = await evaluate(`(() => {
+    const context = new OffscreenCanvas(1, 1).getContext('2d');
+    context.font = '48px ' + ${JSON.stringify(upright?.family ?? '')};
+    const metrics = context.measureText('M');
+    return metrics.fontBoundingBoxAscent + metrics.fontBoundingBoxDescent;
+  })()`);
+  const framed = await json(`__gm.objectRect(${JSON.stringify(TEXT_OBJECT)})`);
+  const frameScale = framed ? framed.w / upright.width : 0;
+  check(
+    'a text is as tall as its face’s line box, with no glyph cut at its top or bottom, and framed as drawn',
+    Math.abs(upright?.height - lineBox) <= 1 &&
+      upright?.edgeInk.top === 0 &&
+      upright?.edgeInk.bottom === 0 &&
+      Math.abs(framed?.h / frameScale - upright?.height) <= 1,
+    JSON.stringify({ upright, lineBox, framed }),
+  );
+
   // 30g. Dropping a font file onto the editor uploads it and makes an asset named after the file.
   const dropped = await evaluate(`
     (async () => {