measure() now is layout(). LayoutContext can either persist layout
information or be used temporarily for measurement. While this caching
is constantly thrown out currently, this is a step towards being able to
only re-layout widgets if they've been invalidated.
I decided scrolling a label would work better, so I loaded a source file
and noticed it wasn't rendering quite right in the label. It turns out
that the text wrapping was triggering despite the width in redraw being
the same as the measured amount. In short: sometimes the width I measure
can't be the width I set as the cosmic_text::Buffer size, because it
will cause it to wrap.
I've worked around it by caching the measured text for now. But it may
still show up in other situations and may require a more generalized
fix by seeing what else we can gleam from the glyphs being measured.
