Sorry for the delay, i tried to make the strike-through face property
support the same line styles as the underline, but i couldn't figure out
how, as it seems that strike-through is designed to support only 1
style.

My solution was to make a kind of hack to display the underline as
strike-through, and it worked.

Another solution was to reuse the code from display space type, for make
a new display property type (as suggested by Gerd), but I ended up
getting lost when I saw too many references to this in the source code,
so for now the hack was the only solution I could think of.

This should work well in both GUI and TUI frames.

In GUI, the line will be displayed as a double horizontal line (as
shown in the screenshot)