Make reflow aware of line rendition attributes

While DECDHL/DECDWL lines are not wrapped at the correct column, now at
least reflowing doesn't clear line rendition attributes, so resizing
Konsole and going back to the original size always recovers the original
content, including double-height/double-width status of each line.

Reflowing double-height lines doesn't make much sense, since a
double-height line actually consists of a top (T) and a bottom (B)
line. Shrinking them could lead to TTBB lines, which look weird. At
least now going back to the original size brings back the original
content in all its glory.