Two cases still drew a value cut off without saying so. A single-line
value at a fixed font size taller than the box (12 pt text in an 8 pt
field) was checked only for width, so it fit sideways and was cut at the
top and bottom. In a multiline field, a character wider than the box
becomes a line of its own, which fits vertically but is cut at the sides.
The single-line and comb branch now compares the line's ascent to
descent against the clip box (a new `Overflow::High`), and the multiline
branch reports the widest wrapped line that is still wider than the box.
An empty value draws nothing, so it is never reported, however small the
box.
Fixes#4018
Ridzzz0Alam
b98d8a2819