label: Never measure more than max-width-chars

label: Never measure more than max-width-chars

Even when we have tons of width available, still do the wrapping at
max-width-chars.

This is what happened in GTK3, too, but it happened automatically
because GTK3 did for_size = MIN (for_size, nat_size) and GTK4 does not.

So we do this manually in the label now.

Fixes the label-sizing.ui reftest.