geom: a called-out label is broken or shrunk before it is dropped

[timzifer]

Why

A label called out of a thin slice at nine or three o'clock has only the margin beside the chart. In a sunburst whose panel is not much wider than the ring, the long names were dropped there — the ones a reader cannot guess from the colour, and the ones a callout exists for.

What

A called-out label is fitted to the room on its own side the way a box label is fitted to its box, in the same order:

1. one line at the layer's size (unchanged),
2. broken over two or three lines where Wrap allows it,
3. shrunk down to MinFontSize, on whichever shape holds the largest type,
4. only then dropped with its leader.

The shape is settled before stacking; labels on one side are stacked apart by half of each neighbour's height plus a pixel (for one-line labels: the same step as before). The leader meets a wrapped block in its middle.

Labels that fitted before are unchanged — golden files and the gallery are the same.

• geom/text.go: calloutShape, per-callout font/shape/block, height-aware stacking
• geom/textfit_test.go: wrapped instead of dropped, shrunk without Wrap (dropped with MinFontSize at the layer's size), stacked by block height
• ADR 0082: amendment; Callout / Wrap docs

Tests

go test ./..., backend/gg incl. gallery (via go.work), go vet ./...

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