This updates the behaviour of Typeface::getStringWidth,
Typeface::getGlyphPositions, and Typeface::getEdgeTableForGlyph to match
the documented behaviour of these functions. Previously, these functions
returned results normalised to a size of 1 point. The new (documented)
behaviour is to normalise to a JUCE height of 1.0 - that is, scaled so
that the sum of the ascent and descent is equal to 1.0.