Extract WrapsText

[smnandre]

TextMeasurerInterface asks for two methods. Only one of them, measureLine(), knows
anything about the font. wrap() is greedy line breaking that calls measureLine() and
nothing else, so every implementation has to write it again.

atelier/diagram did: ThemeTextMeasurer has seven lines of its own work and 78 copied
from CharWidthTextMeasurer, 76 of them character for character.

This moves that logic into a WrapsText trait. CharWidthTextMeasurer now uses it and
keeps only what measures a glyph.

The trait reads the baseline from measureLine('M', ...)->ascent rather than from private
state. Output is unchanged: lines, width, height and both baselines match to 1e-12 across
word breaking, blank text, a zero width and an overlong word.

Nothing breaks. wrap() stays on the interface and the trait is opt-in, so an existing
implementation compiles and runs untouched.